Quoted from metallik:

He easily meets copyright fair use claims for initially making and displaying the game. Problem is, if he sells it he's making money (even if a pittance compared to the time invested), which triggers more scrutiny. However, the biggest problem isn't even copyright, it's trademark violation. You simply cannot make and sell things using another company's trademarks without their permission. Even onesies-twosies. As long as it stays under the radar he's probably fine, but again, once money is involved, things can get complicated fast. Notice that all the Matrix sales have been off the radar, so to speak...