Trivia: Sidney makes a brief passing reference to having a husband named "Mark." After hearing much fan speculation, the directors confirmed that her husband is indeed Mark Kincaid from "Scream 3," who was played by Patrick Dempsey.
Trivia: Originally, acclaimed director Rian Johnson was meant to have a cameo in the film as the director of the fictitious "Stab 8." He would have appeared alongside "Scream 4" co-star Hayden Panettiere as her character Kirby in a short scene. However, scheduling conflicts prevented this from happening. Nevertheless, a photo confirming that Kirby survived "Scream 4" is briefly shown, and Panettiere has a small voice-over cameo during the party scene alongside other cast and crew from the series.
Trivia: MAJOR SPOILERS: Courtney Cox was heartbroken when she read the script and saw that Dewey got killed off, since he was such a likeable, positive character. She tried to talk the directors out of actually killing him by throwing in a last-minute twist that he was still alive, such as her getting a text from him at the hospital and revealing he wasn't the one in the body-bag. However, she ultimately agreed with their decision to kill him off, since it raised the stakes.
Trivia: When the group of friends are first introduced, if you look closely, Wes and Amber are snacking on a bag of grapes. This is a bizarrely specific reference to a scene from the first film, in which Tatum and Stu are also seen snacking on a bag of the same type of grapes. SPOILER ALERT: Just like in the original film, one of the people eating the fruit (Amber) is one of the killers, while the other person (Wes) is a victim.
Trivia: During the scene that reveals Kirby is still alive via YouTube link, if you look very closely, you can also see a link to a YouTube conspiracy video called "Did the Real-Life Stu Macher survive?" This is an easter-egg referencing a popular fan-theory that Stu actually survived the original film and would return as the killer in a future installment.
Answer: As far as I can tell, It's never stated in the movie how he found out about that. Maybe Sam told him off screen when he "learned " that Billy Loomis was Sam's biological father.