I would say that you quite possibly hit him in the jugular vein and the shock of the bullet stunned his spinal cord and he just bled out.
A 212 grain bullet is what might be called big for caliber out of a 06. Sure you can find 220 grain and larger bullets for a 06 but performance falls way off when shooting them. A .300 magnum has the powder behind the bullet to keep it going where a 06 doesn't.
The shot was in the chest just behind the shoulder. I had suggested the 200 grain instead.