We are supposed to be the reality based community, so I decided to take a closer look at this video. I downloaded it, blew it up, and watched it frame by frame, over and over again, and I can say I am 90% sure Bush was giving a thumbs up, not flipping the bird.
The resolution and frame rate of the video makes it difficult to be 100%, but I took a couple of screenshots of frames I think make it clear it is his thumb.
See across the bump for the images.
This is the best frame for showing it is not his finger, but admittedly it isn’t that clear. Note how thin his wrist is. This indicates we are seeing the side of his wrist, with his palm facing left. That would be impossible if this was his middle finger. His fingers are curled around, and you can see his knuckles on the left of his thumb, making it appear that his thumb is in the middle of his hand. The perspective in some of the frames is such that is thumb appears longer than it really is. Try this yourself: Palm facing left, thumb up fingers curled in. Now raise it above eye level in front of you, keeping it in the same position with thumb up and palm facing left. Your thumb is in the middle and looks extra-long, doesn’t it?
This is a sequence of Bush lowering his hand:
These frames show his hand rotating, so in the last image the finger/thumb is pointing left and is on the edge of his hand. This would be a very awkward maneuver if it was really his middle finger, but very natural if it is his thumb. The fact he is rotating his hand is more clear if you watch the video very slowly.
