Awkward situation

[HitHard69]

Home game, 1-2 No-Limit, starts raining out, and one player "Paul" goes out to roll up his windows and says "somebody play for me." Very common in our games since we all have basically the same pre-flop standards...any bets/raises we wait for the player to come back. Anyways, UTG+1 folds and plays for Paul. 4 to the flop, including me. Except when UTG+1 looks at Pauls cards, he exposes them to a player in the hand. Player in the hand says he only saw one card. Myself and the other player in the hand say that we get to know what the card is. At that time, Paul comes back in and we tell him what happened. He says fine, and the player who saw the card says he saw tha ace of clubs. flop come 4,7,K. I fold, player who saw Pauls card folds. HU between Paul and one other player. Turn and river are unimportant, except that each brings a $10 bet from Paul and a call from the other player. Player turns over 2 pairs and thinks he won becasue Paul didnt match his ace and so couldn't have better than a pair. Paul turns over pockets 4's for a set. Apparently our buddy thought a 4 was an ace. Paul insists he did nothing wrong and the other player in the hand says he was being nice and just calling instead of raising when he knew he had the best hand. Guy who's house we are at tells them to split the pot. They do, and then both cash out and leave.
Any suggestions on the best way to handle this? Personally, I think it was an angle shot by Paul. All he had to do was say "You didn't see an ace." Then again, it isn't his fault someone else saw his cards.