The argument about strictly speaking ahigh-powered slug "knocking an animal off its feet" is really no more relevant than .... "how many angels can balance on a head of a pin."
What counts is how much force, bullet expansion and controlled damage can be delivered to make the deer, elk, bear, whatever loose blood and consciousness as quickly as possible to bring it to the ground and expire.
That's the bottom line.
The shock to a deer’s system delivered by a high-power rifle in key places can an often time will bring it immediately to the ground. The rest is a nice academic exercise.
But if you enjoy that, it's okay, too.