Strange occurance on birds of prey

[Robotic Pope]

No. Never happened on xbox anyway. If I'm right in that you can't invite on Ps3, that rules out the "invite from search" wrong game mode glich. Was he on the matches scoreboard? I guess it could be a simarlar kind of bug that makes your game think its in a dogfight, but that doesn't explain how he appeared without being in the lobby. Are you sure he didn't just join and ready up a split second before you started the game?
The only other possiblities are a hacked game, or some kind of weird connectivity problem between yours and his PS3 causing the game to get confused.