Other mistake: In the DVD booklet, two errors are made for this episode. The booklet says Homer accuses Bart of ruining Thanksgiving and Bart was jealous of Lisa's centre piece. These are both incorrect: First, it wasn't Homer who accused Bart of ruining Thanksgiving, it was Marge who accused Bart of ruining Thanksgiving and second, at no point throughout the episode was Bart ever jealous of Lisa's centre piece.
Other mistake: While Kent Brockman says "This reporter smells another local Emmy" after he gets back into his van, his face is drawn incorrectly.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.