I’m in the US and, due to the wonders of the American healthcare system, that will impact the answer.

I’m a desk jockey - I write code. For the holidays, I got a fancy new mechanical keyboard. While reaching under my desk at work to plug it in, I pulled a back muscle so hard, I basically could not move.

I took Advil and waited, but it just got worse. I finally called my HMO’s advice nurse line and as soon as I mentioned I was at work, she suddenly stopped asking me about my symptoms or giving me advice, and started talking to me about workman’s comp, how this could be my employer’s responsibility, etc... she basically became a wall. Frustrated, I just hung up and went to urgent care (I slooowly got in my girlfriend's car and she drove me).

A couple muscle relaxants later, I’m basically OK, but my question is, why did this happen? If my job were moving boxes or handling heavy machinery and I got hurt, then sure, I understand how this could be my employer’s responsibility. But in this case, I really don’t see it that way and I couldn’t get anything out of the advice nurse. Does merely getting hurt at work even if it has nothing to do with your job mean it’s on the employer?

In the end, I am just really annoyed that before getting relief for the pain, I had to go through

• Where did this happen?


• Did you tell your employer?

etc...

First and foremost: I am not a lawyer.

You're in the U.S., but you don't say what state, so I'll speak from my experience (having been in your exact situation) in Ohio, but you might have a different experience (for example, California has much more pro-worker workers' comp laws).

First: report the injury to your employer. Regardless of whether it qualifies as workers' comp or not, they will need to be aware. If you have a large employer there will probably be a dedicated person on staff who will start handling these things. Additionally, your employer is most probably required to report the injury to a state-level BWC office. In Ohio, an employer is required to report the injury to BWC if it caused 7 or more days of disability (that does not just mean "time off work") or death.

Second: you'll be assigned a case-worker, talk to them. They will help you. Once you get a case-worker their job is literally only to get you help. Call them, talk to them, tell them what happened. Ohio has a huge boatload of rules about what you, your case-worker, and your employer must do.

Third: in Ohio, most injuries you receive at work are covered. Here's a human-speak version that isn't as lawyer-ey:

Back injuries – U.S. workers often complain of lower back pain caused by the strain of lifting heavy objects while at work. Whether the injury was caused by a blow, jolt, or sudden stress, or if it developed over time through repetitive movements and carrying heavy objects, you may be eligible for compensation for herniated discs, fractured vertebrae, sprains, strains and other problems.

Directly from the Ohio BWC (emphasis mine):

Under Ohio workers' compensation law, when a claim is filed with BWC, all medical conditions requested in a claim are considered alleged until a determination is made either allowing or disallowing them.

And (again, emphasis mine):

Allowances are medical conditions recognized as directly resulting from a compensable work-related injury or occupational disease. Allowances are supported by medical documentation submitted by providers. Allowances are also referred to as allowed conditions and allowed diagnoses.

If your state is anything like that, what it basically means is that the BWC (not your employer!) will decide what claims are "allowable". As an example, I tore an inguinal hernia doing a task that was loosely related to my job description, and I was in fact not obligated to do said task, but BWC took the injury as an allowable claim, and they paid for all of my medical expenses.

Edit: you say you are in California, so there's a whole (well put-together, I should add) booklet that talks about your benefits and such:

Workers' Compensation in California: A Guidebook for Injured Workers

I want to highlight this part (emphasis mine, from page 7):

“Accepting” the claim means the claims administrator agrees your injury is covered by workers’ compensation. If your claim is accepted, you will receive paid medical care for your injury. You may also eligible for payments to help make up for lost wages. To learn about these payments, see Chapter 5.

In California, much like Ohio, you don't decide if it's an eligible workers' compensation claim: the state does. So, while you may think "it's nothing", you still may be eligible for the full coverage of the medical costs you incurred (I suspect they're not particularly high, but still not 0.)

So, to answer your question:

Does merely getting hurt at work even if it has nothing to do with your job mean it’s on the employer?

While the burden to pay may or may not fall on your employer (read: employer's insurance company), neither you nor your employer make that decision: your BWC office does (read: can). Your office will weigh all factors of the case (including whether or not there is a reasonable expectation that you would have to do this type of labor on a regular or irregular basis) and make a judgment.

You went under your desk to plug a keyboard in. You are using that keyboard for work. If you don't plug it in, you can't do your job. OF COURSE this is a work related accident.

Helpdesk nurses are in the awkward position between healthcare and helpdesk, she probably has a script she has to stick to.
The "got hurt at work" box on that particular flowchart likely only has one line going you of it: "The guys from Legal will chew you out if you say anything here"

Because, even in more civilized countries, getting hurt at work lands everybody involved in a massive legal quagmire of responsibilities.

In this case you probably should have called someone in the company, usually there are designated people for all first-aid related issues.

If by "why did this happen", you mean the response of your HMO's nurse (rather than the injury itself), the answer seems simple and rather obvious: the HMO wants your employer (or their insurer) to pay for the cost of treatment.

Does merely getting hurt at work even if it has nothing to do with your job mean it’s on the employer?

It can be a legal minefield but generally yes.

Circumstances and laws may change that to a no (your fault or company not liable) or a hell yes.

For instance:

• Did a supervisor say you may or have to plug the keyboard in?
  
  


• Does the company have an IT department that does these kinds of things?
  
  


• Are you allowed or prohibited to alter company equipment?
  
  


• Did you inform your employer right away about the incident?

Disclosure: I'm not familiar with U.S. laws regarding this.