Continuity mistake: When Homer is talking to the makers of Police Cops, the person on the far left's hair changes from brown to grey instantly between shots.
Continuity mistake: The name card display stand on Homer's desk disappears after Mr. Burns interrupts him.
Revealing mistake: There are two Ruth Powers in the same shot, when the people are crowding on Homer at the mall.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.