I don't think a simulation needs to simulate anything real. Eg. if I have a program that runs Conway's game of life, that would be also be a simulation, but there's nothing "real" it references against.
In other words, the universe simulating ours might work completely differently, and some beings there are just testing how different laws of physics (i.e. ours) work out.
In other words, the universe simulating ours might work completely differently, and some beings there are just testing how different laws of physics (i.e. ours) work out.