utg is laggy. He might have just top pair. If he had a set, he would likely be inclinced to sit between 2 preflop raisers as they fire back and forth, so he can collect lots of bets in between them.
Then again, at 3-6 you run into lots of random guys, some of which grossly overplay their top pair, and others which pee their pants when someone raises them and they have "just 2 pair".