I'm not so sure it's an accumulated affect - just a very heavy hit with no give (ground impact).
When they showed it, I think Burton was pissed at the hit (for some reason?) and as they landed his forearm/fend slammed his head into the turf like he was grounding a try.
Not implying he meant to intentionally hurt him, but his head had nowhere further to travel having hit the ground whilst the brain continued its momentum towards a stationary skull, meaning the meninges had far less impact absorption.
Dr TurnStyle