Matt had been cheating on his girlfriend. Too bad for him that she found a cursed board game, and knew what would happen to cheaters. She knew that he always cheated at boardgames, and couldn't resist to do so on tonights game night.
Matt of course moved his piece when he thought she wasn't looking, and as the green smoke poured from the board, he could not only feel himself changing physically into a monkey, but mentally too.
He would of course change back once the game is finished. Too bad that his girlfriend packed up the game and threw it to the bottom of a lake. Hopefully the local zoo will take a new monkey.