Its true. The length of his limbs is throwing us off a bit. However, I think a couple of the reps in the vid had acceptable starting position but you are driving your hips/ass up without straightening your back at the same time. So you're getting right back to that bad position with your hips too high just a bit later into the pull. The straightening of your back and the straightening of your legs should be coordinated so they are happening at a pretty much the same time and rate.

IW