Creationism says “there was nothing other than something that always existed (don’t ask how it existed), and then it created this universe.”
Simulation theory, particularly ancestor simulation theory, says that a chaotic universe very similar to the one we find ourselves in spontaneously came to exist with or without design, but that eventually that universe reached a point where it could simulate itself and we’re in that copy.
The first requires an intelligent being effectively pre-existing everything else. Simulation theory allows for the intelligent beings creating our particular version of things to have evolved from everything else having existed first.