Well spotted! It appears that
this account has indeed changed hands as the email address was changed on July 22, 2017, alongside with posting and IP patterns.
I've now locked it!May I ask why? Account sales are not against the rules:
account sales are discouraged.
Is this a new policy?
Do we know for sure that it was sold? I will unlock it if he will be able to prove that it wasn't hacked by going through the recovery process, however, my "hacked" radar is off the charts

In the past, theymos has had a fairly high threshold to lock an account out from the person using it.
I am not 100% sure what the standard is however I suspect someone would need to show a basic evidence they are the owner and at least a statement from the person their account was hacked (so they would be lying if they sold it).
IP patterns also change for various reasons (such as traveling), but devices remain more consistent so I hope IPs arent the only thing you guys look at.