Interesting that his hands go down to "release" - pause- then move back up - before continuing down through impact. Essentially one of the shortest backswings in history!
If I had to guess - it looks to me that at one time - he was taught or read that a delayed release is how you make a correct or powerful swing. His intent is to get into that delayed release "position" - and then he doesn't know what to do with it. I'd say the head movement down is a result of that delayed release effort and not a primary thing to work on - however certainly could be part of the equation - as it's part of the fabric of the delayed release effort. Why does he continue to make that effort and not try something else - because in his mind the delayed release is a requirement - a fundamental - anything else in his mind would be throwaway/hacker move. Position golf gone bad.
Can everybody just leave this guy alone? He has a hard time swinging a golf club...it was funny like 5 years ago...now it's just tired. Let. It. Go.