IPF (my fed) allows thumbless on squat.
My point isn't about thumbless grip. I've used that before with some success before it caused pain in my hands.
My point about pulling the bar down on your back refers to the fact that his hands are open and his wrists are cocked. How can you pull the bar down with open hands like that? It looks inactive like they are just a handy place to rest the bar rather than an active part of the squat.