Lets start with the easy stuff.
It's pretty hard not to acknowlege the rocks in the vents, but if you think that proves he landed on his head, I think someone has rocks in his head. You cannot get a good view of how how landed beyond the barrier, but it sure looks to me that he didn't land head first.
I've had experiance with this type of crash. 2 of my last 3 crashes were somewhat similar to this one. I had been looking over my shoulder for traffic coming up in a tricky area and when I looked ahead again, there was a wrong way rider directly in front of me. Now, I didn't hit him exactly head on, but pretty close and I did a flying arial landing on my back a number of yards away. More recently, I had a BMXer pull directly in front of my path at a right angle so I contacted his rear triangle with my front wheel and did a 180 that seemed the slowest flip in the world. I remember thinking, "OK, now lets see if this helmet works out like everybody on the boards have been posting about". I landed on my back, got up and the first thing I did was take off my helmet and look for damage. Guess what? Not a scatch. Just like the previous crash where I did a flip. I looked at the BMXer, saw he was OK and the first thing I said was, "See this helmet? Not a mark. All those stories about needing helmets and them saving your life is b###s###t"
Point is, Kessler may have had rocks in his vent but that doesn't prove he landed head first, just that his helmet did roll around in loose gravel. As best can be shown in the video/pictures, he was lying on his entire body.
Now for the other part, maybe we need a third party here or maybe one of us needs new glasses, but it's evident to me, that the rider did not slide on his head nor hit the barrier with his head. he slid and hit as I remembered and posted he did. If I don't need new glasses, maybe someone else does.