Actually it's a reality check about physics. MxV=F
Mass times Velocity equals Force.
If his head hadn't split open, could his neck absorb the impact?
The helmet argument as the end all of motorcycle safety is a fallicy. Besides, we don't know if the rider involved was at fault, or if it was a mechanical failure, or an unattentive driver.
Bottom line, at that velocity, his cranium took the brunt of the force.