He changed his deck. It was when we were checking decklists and caught it.
When I pointed it out he said "so?", to which I responded that you can't have more than 4 and to go change it. It was the 2nd funniest moment of that day.
The most funny was when we were doing deck checks and someone had a fake Dragonite card. We pointed it out, and he said "so?" as well. (Before you ask, it was a different person.)