I found a debunker link specifically aimed at this video, but I'm not sure it's any faster to look through this than it is to watch the video:
I also downloaded the newly released security videos. It's not movie-speed frames, couple or a few frames a second. All you see is part of the fuselage for one frame and then the fire and smoke.
I remember at the time that United 93 went down I thought it must have been shot down, even after initial reports stating otherwise. So I can see how people might form their own opinions.