I have no idea what he means either, but if it helps, a "cop out" is sort of a rather cowardly, less troublesome and not really rewarding way of solving a problem. Example - so you've made a big effing plot twist, your player character is in a huge mess, and there's simply no way to solve it because the game's running VERY long as it is. Cop-out: cliffhanger ending (Simon 2, anyone?). The "It was all a dream" ending can also be seen as a cop-out.