I think he would benefit from working on glute strength.
Pull-throughs, jefferson squats, glute-ham raises, reverse hypers, etc. . .
Lots of options there, but, overall, cutting the weight back to focus on form more and adding some hip strength (glutes especially) specific assistance work would help him, IMHO.
It looks like he locks out with lumbar hyperextension to some degree because his glutes aren't strong enough to finish the movement.
I think that can be addressed by doing high rack pulls and holding the weight at the top position. Maintain a good lower back position at that point and squeeze the glutes. I've heard of people doing this to teach the body to lock out with glutes instead of low back.