Strange Claims

we dont play omaha once, but after a few of us got out of our main one we decided to play a quick omaha NL.

the board was something like 39944 and 2 of my friends went all in. one had AA2K the other had KK95. kk95 saw it and started taking the pot with his trips but then the other guy said- no! the best hand there was a full house but since you can only use 3 cards you couldnt have a full house! so that means you have to use your kings and i use my aces, so i win! we didnt really know what he was talking about, and he was pretty stubborn but after showing him proof a day or so later he paid the winner.