Yeah, I noticed that too. Not looking forward to playing them with their level 16s.
I remember seeing a bug report that someone on a different team saying they had gotten double XP for a game. If I had to guess, I'd say it was that. The devs did what they do: swept it under the rug saying it is too rare to happen again and that they can't do anything about it anyway.
http://goallineblitz.com/game/forum_thread.pl?thread_id=4737890