Exactly. Thanks for succinctly expressing my point better than I could.

The question is whether assuming a correspondence as a somewhat default case (implied by the "not necessarily") is even a good default assumption.

Why would the rules inherent in what we see inside the universe be any more indicative of the rules of the computer simulating that universe than the rules inside a computer game are reflective of the instruction set of the CPU running it (they are not)?

I am aware that the reference class "computer running super mario brother / kirby's dream land" implies for the rules to be different, but on what basis would we choose any reference class which implies a correspondence?

Also, I'm not advocating simulationism with this per se, the "outer" computer can be strictly an abstraction.