Factual error: As Bart, Homer, Ned and Todd drift away from land in their boat, we see the clouds moving away. The clouds would not move that fast at the speed that the boat was going.
The Boy Who Knew Too Much - S5-E20
Factual error: Apu (an immigrant from India) could not have been selected for the jury because he is not an American citizen, and this was before he became a naturalized citizen in "Much Apu About Nothing".
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.