I was just in a game where my opponent bailed, and I forced him to resign 5 minutes later.
Suddenly, I was spontaneously in a game against Lord Rattington despite not requesting a bot game.
Joining game #48790 on frankfurt.
Amweisgerber left the table.
Joining game #48984 on oregon. (this was the bot game)
Okay, this seems to be related to being Ready with nobody else at the table.
Yes, when you ready at a table with to few opponents, the empty slots will be filled with bots.
This managed to happen when I wasn't clicking ready though.