RE: Why did he die so quickly?
Whole a solid liver hit can be quickly fatal on a high shot like that where you know you were up near the spine I'd be on hitting that artery. Especially since you heard a lot of crashing. With heart shots and major artery shots there is no blood getting to the brain so the deer run into trees and brush a lot while they are kind of on auto pilot before expiring.
I shot a doe last year and severed the main artery in the back and her spine on a high shot. She fell and bled out in 8 seconds as I watched.