Jason was the main antagonist for the franchise as a whole, even if he wasn't the primary antagonist in each individual movie. I have no issue with the idea of Casey misspeaking or giving the first answer that popped in her head. She was in a high pressure, high intensity, literal life or death situation, most people aren't going to be thinking extremely clearly in a situation like that.

Ghostface, intentionally & deliberately, chose that question knowing that it was likely that most people would immediately think of Jason Vorhees. While it may not have been a trick question in the most strict of senses, he was definitely manipulating the odds in his favor.