Well, it's fairly obvious the team didn't know he was back, but he could have hidden out in his room (maybe sleeping?) and they might not have noticed if they'd only been there briefly.

Or he could have gone anywhere. Gone to see someone. (Alain? *g*) Or... I don't know. But it could have been quite a while.

Or yes, he might have just wanted different clothes. Though he looked pretty fresh and clean in that last scene of LotTL.