Comment by Tuna-Fish

He has a writeup of it here: https://eieio.games/blog/writing-down-every-uuid/

He's using a bijection between the number on the left (which are ordered) and the UUID that's designed to produce something random-looking. The simple fact that bijection cannot produce the same output out of two inputs (or it's not a bijection) means that all the UUIDs are unique.