Home Game Horror Story

Up until maybe 4 years ago, my buddies and I were playing poker almost every night. Usually 5 card draw as thats what most of the group knew how to play. Anyway, we were playing with one of those decks that was actually used in casino play (you know the ones that have holes in them that you can get for like $1 at the casino). During one very large pot that thankfully I was not involved in, the two remaining players were betting at each other like crazy. The pot is up to around $70 (which was huge for us at the time). Finally it is time to show down. Player 1 flips quad 5's, and player 2 flips a full house Aces full of 10's. Thats not the wierd part though..... one of the other guys at the table screams "hold up". He flips his mucked hand and shows that he had a pair of 5's. One, what do you do in that situation? And two, how was this deck used in a casino? Since then, we always check our decks pre game.