IME (once upon a time) the gas doesn’t get very cold. The canister gets cold cause the gas takes heat from the canister as the gas expands (cause thermodynamics). By the time it exits the whipping cream container it’s expanded enough that a small (lung sized) volume shouldn’t frost anything.

I’d guess this kid popped a nitrous cartridge directly in his mouth or without much of a intermediate vessel or blew the whole thing in his mouth at once.