Hard to tell in a video due to the lack of 3D perception, but it looks like the scapula is winged out, which would be consistent with a damaged/destroyed rhomboid. It would still be possible for some of the rhomboid to be intact, helping maintain function. The Levator Scapulae would remain intact. Pretty much all the other scapular muscles attach forward on the rib cage and leg. I'm basing this off of human anatomy, so I could be missing something.
Blunt avulsion injuries don't always bleed much as the tearing follows the facia and few blood vessels are transected.
The wound looks very fresh, making it more likely that compensation mechanisms have not had time to be exhausted. The movement of the avulsed skin would represent an amazing attention to detail for a fake.
I have seen function remain with some crazy injuries in people (I have also seen function lost with what appears to be a minor injury), so I can believe that this is real.