Cheating?

I think this person might have been cheating, which is something I have never accused anyone of on this site.  I really felt I had the upper hand, then they left for 15 minutes.  I assumed they were not coming back, so started another game and won it quickly.  When I was in the middle of the rematch, this person came back and they stomped me, despite the large rating difference.  I barely pulled the other game together after blundering in that, too.  Maybe their tactic was to wait for me to start another game?  They got a huge rating boost with this one, but mine should go back up and their's back down.

No naming and shaming. No talk of cheating on chess.com. Cheating talk is restricted to this group

http://www.chess.com/groups/forum/cheating-forum

Mod.