Earlier quoted context omitted.
I didn't downvote any of your comments, but I didn't understand your gripe until this post, and I agree with you that the question is not worded well. Imaginary's primary definition is only existing in your imagination , so it's technically correct on one level, but if you look at synonyms for imaginary, and the way that people commonly use it, you get words like nonexistent, made-up, fictional, unreal, etc..
So nonexistent pain hurts as much as real pain? Doesn't that make even less sense?
Most people in this thread see it as real physical pain conjured up by one's imagination - so things like psychosomatic pain, pain caused by mental illness, pain caused by fears, etc. So think of someone getting dizzy from their fear of heights, or a hoarder doubled over retching because someone is throwing away parts of their hoard.
Whereas you in essence think that it's an oxymoron - if it's real pain, it by definition can't be imaginary. So it's just a thought exercise or a theatrical performance.
So maybe the sentence would be less bullshitty if it read "irrational pain" or something like that.
But as most people read "imaginary pain" as "real pain felt, without reason" instead of "fake pain you're just imagining about", I think your reading of "imaginary" is too parsimonious.