How fast your sprint is a function how much backward force there is. You don't drive "down", you drive back. Try driving down and you will see it's impossible to do with any kind of force without the heel touching the ground.

Thanks for the video. The guy in the assistance crew is in fact heel striking. It's not classical extend your leg to hit the ground and roll novice runner kind of heel striking as his leg already moves back and his knee is already bent when he hits the ground but he does hit the ground with the heel first.

I wonder if it's because of the shoes. I don't think he would do that in flats/track race shoes.