That particular video isn't about perfect squat form. The kid should be able to keep the proper back angle all the way through, but he doesn't. But what he IS learning is hip drive, so his form will "good morning" as well, if slightly. You'll notice he did maybe one squat with good form in the video, where the squat was very fluid and not compartmentalized.
If you're driving with your quads mostly, then your legs will straight out before your chest has become upright. Hip drive is what balances out the squat, because of the way you have to (or should) be sitting back to accomplish it.
That Ed Coan video is a great example of really utilizing hip drive.