Factual error: The cover of "World's Finest Comics" #94 is shown on the wall at the comic book store. It features Superman with a sign that says, "Gotham or Bust," and Batman gulping. The actual cover of "World's Finest Comics" #94 shows Superman being sprayed with liquid kryptonite while Batman and Robin catch sight of him.
Continuity mistake: In the surgeon's office there are three certificates on the wall with ribbons on them. In the first shot there are two red ribbons and a blue one but in the shot where Homer stands up to read the bill all the ribbons are red.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.