When the car he hit slowed down, he probably fell forward off the roof and then was run over and killed by the car he hit.
I could happen...
I remember many years ago, my buddy and I were riding our Bridgestone 175's out on state land. We were on a gravel road on the way back to the main blacktop road when my buddy hit a deer. We were going about 50 mph when he hit the deer. The deer was knocked out I guess and was draped over the front fender. We rode that way for what seemed like a mile, I'm sure it wasn't, but time slows down as they say. When he slowed down the deer fell of and got tangled up in the front wheel and down he went. He broke his arm in the process. He was due to be drafted the next week and got another couple months delay in going into the Army. I guess when I said "draft", you can guess this was not just a few years ago.
Anyway, I hope the guy in the video didn't get hurt on the way down.