Continuity mistake: At the beach when Zach and Laney are leaving it is sunset. In the next scene at Laney's house it is mid afternoon at the latest. It has to be the same day because they attend a party that is mentioned as "tonight".
Other mistake: When Laney goes to the beach she's carrying a huge book. When they leave the beach, there's no book.
Answer: The appearance was a cameo only. It was not that random though, as the scene was shot at a location also used for Buffy The Vampire Slayer, and Sarah Michelle Gellar's husband appears in the movie.
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