It’s a good question. But I can’t say I know the answer. My devices have fingerprint biometric unlock and I don’t walk away from my laptop without closing the lid usually.
I work in the bitcoin space for 6 years now, so I wouldn’t put it past someone to be able to pwn me. But it’s most likely the Password Manager hack and my lack of changing passwords in a timely manner that did it.
Not sure if this helps, but here’s how I usually prove my identity on various platforms:
https://github.com/offordscott/1scottQvCoZ8eCjkMscbbWbAZJ49eizsE/wiki/Check-for-Valid-SignatureScott
Do you have anyone close to you that knows about Bitcointalk since you said the post weren't made by you?
Because someone around can be the closest who can do such thing probably such user is dreaming to have a big account, or could be as a result of of autosave password.