It seems to me that someone guessed Gleb's password using the password hashes stolen in 2015, since Gleb didn't change his password since then. The Glebonator account may be due to the attacker trying a new password-cracking attack against accounts in alphabetical order, or due to specifically targeting Gleb and incorrectly believing that that account belonged to him, or because Glebonator is the attacker.
I still don't see the ones that were sent to me in my In Box, but that may not be important I guess.
I restored those as well now.