Corrected entry: When the entire school is banqueting after their arrival, D. Malfoy says: "Potter. Is it true you fainted. I mean you actually fainted?" In the book, he found out because Neville was in the compartment as well, and he told "nearly everyone." But, in the film, only Harry, Hermione, Ron, and Professor Lupin are in the compartment. The three friends wouldn't have told them, and a schoolteacher doesn't go around telling such things to students. So, as Harry himself asked, how did Malfoy find out?
OneHappyHusky
10th Jun 2006
Correction: There are large windows on the compartment facing the hallway, which showed considerable traffic previously and in the other movies because the snack cart was located farther up the train. It is reasonable that someone saw what had happened during the time that Harry was unconscious or was alerted to the scene by Harry's screams, that Ron discussed.
OneHappyHusky