What was wrong with his back angle in this video?

[SBegetis]

http://youtu.be/UTSvYD3K91Y

I understand from the book that lifting the chest kills power out of the hole, and kills hip drive and your hamstring tension. I've been told through technique feedback on this forum that I try to be too vertical on the descent, which causes me to lose the back angle on the ascent. As if my knees and hips go back instead of up. What was the athlete doing wrong in terms of his back angle? I know you have the eye to see it from a mile away, but I'd like to understand how to catch too vertical a back angle so it can help my training. Was it his ascent? His descents? Which reps looked best? Which were worst/most vertical?

[Mark Rippetoe]

I saw it in his descent, trying to maintain a chest-up position that exaggerated the knees-forward at the bottom. Rep 1 and 4 were the worst.