> he's still responsible for the theorem being proved.
I think you have an odd definition of "responsible". Many (most?) theorems start out as conjectures, and I would strongly disagree that just because someone first formulated a problem that they're "responsible" for the eventual solution.
It's not just that he formulated the problem, though. It was specifically the fact that he claimed he had a proof which led to the proof, and it was only because people credibly believed he had one that they spent so much effort trying to (supposedly, re-)discover it.