I know I can't explain how it's wrapped, but when you have your rifle slung the right around your forehand, you're naturally going to want to try to rest your fore-elbow on your body, preferably as far away from your diaphram as possible.
As for the backward stance, that's just the way that shooter prefers it. Apparently, his weld makes him aim low, so he shifts his body to correct his natural point of aim. Once you get into long range, you'll find that you have to make your body get to the point of aim, rather than your bringing your eyes to it. The latter technique causes an unnatural, shakey, point of impact because your body is struggling through the shots.
My best suggestion is to go squirrel huntin with a fixed power scope on a 22lr. Avoid using trees, sticks and logs as support, and try to mae all your shots offhand. You'll naturally develop much the same style as the man in the video, if you're truly hungry for a squirrel.
Hey! Don't laugh, I'm serious!