Trivia: When Michael Jackson did a guest spot on the show he did his speaking lines himself but when it came to singing, a Michael Jackson sound alike or impersonator stepped in and sung the lyrics to the songs. The reason was based upon his record contract, which since he is so famous probably has a lot of stipulations when he lends out his voice.
Trivia: "John Jay Smith," credited as a guest star at the end of the episode, is in fact Michael Jackson, who starred as the man who thought he was Michael Jackson under a pseudonym. Michael is a massive fan of the show and also co-wrote the Simpsons' early hit, "Do the Bartman."
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.