It means the the owner was able to prove that the account is theirs (e.g. via e-mail address ownership, or a signed message) and regained access to their account, which was presumably hacked but I can imagine that an unscrupulous account seller could also steal back a sold account this way so it doesn't really prove much. The message itself comes from
seclog.
OK, I looked at his post history and saw that he started out posting in German and English sections, then switched to the Philippines section on July 30,2017, then switched back to German on May 13, 2020 with
what looks like an account recovery post (I can't read German). That's definitely not enough evidence for me to tag him for account selling.