Hmm, I wonder if I’ve been looking at these requirements all wrong then. If a year of work experience is about 2000 hours, maybe what they’re really saying is they want someone with 8000 hours of experience, which I guess is possible in 1.5 years.

No, it's just HR being HR. They don't know what they want.

It's worse than that, HR is hiring for someone else. I think there are valid cases where someone doesn't know what they want, but can't think of an example when it's acceptable to "not know what is wanted" when that's the sole purpose of your job.