The weakest components of the rifle is where the pressure was released. The mag obviously doesn't fair well, but do you think any other parts were damaged?
It looks to me like the machined parts of the upper are able to withstand more force than the mag resulting in the mag breaking apart, causing all the force of the explosion to be channeled down saving the dude's face and hands.
Was the mag specifically designed to be weak in case this very thing happened?
Obvoiusly I don't know much about AR's, but that was very interesting.
(I would never wish that upon anyone, but since it happened and was video tapes, I definitely want to learn from it.)