We don't. But we can assume that they aren't for the purpose of discussion. It seems more likely that a victim would post the OP's post than a perpetrator.
Google also doesn't, but they can say with increased confidence what the probability of the OP being a victim is.
But there's an even hard problem: say person A sells their Google account to person B, and does this with completely offline communications (offline wrt Google). To Google, this situation may look no different than a stolen account, at least for some period of time. But person A is a scammer, claims their account was stolen, and attempts to initiate a recovery process with Google.
This situation is the reason I virtually never perform account recoveries for players of my games. I also require users to use a third party login (like Google or Facebook) for their account, because I want as little to do with account management as possible.
I think usually it's obvious for someone who can see the account's recent activity. You can also design challenge-response type questions for the person claiming the account, that only they could know, within some reasonable confidence interval.
Not kidding - How do we know you are not the hacker ?
In future please use 2F authentication otherwise there is really no way for anyone to tell who is the right owner.