Should be easy to prove
How is proving an account was hacked "easy" in any way? IP logs are not considered (nor checked, I believe), and the owner could easily pretend to be hacked and then sign an address to say he wasn't.
The reason why I'm pretty doubtful that he got hacked in the first place is that a hacker would (normally) use the account in more profitable ways than to voice a petty opinion in a matter that won't even matter in a couple of years. Selling the account is a common thing that happens; profitable, quick, and easy.