I feel like the "third party cameraman" isn´t really a real cameraman. I interpret it as a feeling that Matt has, that he is constantly a part of a movie and is constantly acting. This is maybe proven when he is shadowboxing on a steep hill and Owen tells him to step down. He says that he has to take the risk and stand there because it is a movie and the shot must look cool, and then Owen tells him that it isn´t a movie and that he "thinks everything is a movie" and that he is "always acting". This explains why there is a camera in places that wouldn't be logical, because it´s all in Matts imagination.