The video is a bit deceptive. The interview that trump did on 9/11 that they show a picture of at the beginning is not the interview we are hearing. In the interview where he took the questions that morning he was asked the same sort of questions and having it just happened and having been put on the spot that very day he said it was the planes and probably the gas. It was a guess and he was put on the spot to guess so it was more like (well they fell after the plane hit them so yeah) we all thought that at the time. But the interview being played came from sometime later after he had time to think about it. Just wanted to point out how the film is slightly deceptive in that it would have you believe this conversation took place on 9/11.. even shows a picture of that interview and plays audio from another.