Look im no expert, but the courses I took in medschool about brain trauma tell me that the momentum from the slam was only so amazing due to the "accidental" headbutt, that what caused aronas head to go to a sudden stop.
Our brain is immersed in fluid, so when our forehead hits a wall, its the occipital lobe that will receive the most damage (the area near the back of the head).
When the area on the back of our skull hits something the pre frontal cortex is the area affected, thats an important distinction, because the way arona was "out" he was more stunned and confused than completely KOed, which means the back of the brain suffered the most trauma
Which means most of the KO element came from the stun the headbutt caused and the follow up punches led to the complete KO