LOL! I only looked at the pictures once, but from what I saw, I can't picture how he fell with his face facing that way with his body landing where it did.
Looks like he fell in a prone or nearly upright position. One of the palings went up through the base of his skull, while his body was on the side of the fence he was facing. The momentum of his falling body was enough to separate it from the head, which stayed put.