Cartman tells Kyle that The Passion of the Christ (2004) is the highest grossing film ever made. Titanic (1997) is in fact the highest grossing film ever made with over 1.8 Billion US dollars made. "The Passion'" is the highest grossing non-English film ever. But Cartman is an idiot, so it could be a deliberate mistake.
At the beginning of Cartman's fan club meeting one person asks a couple at the table if they are the ones who are running the meeting. A minute later this same man says that it is great that the meeting is being called by an 8-year-old who was moved by the movie. So he already knew the couple didn't call for the meeting.