The way I think about this point is that it's a sort of computational ceiling for physical processes
The resources required to simulate the rock this way is massive overkill. It's probably massive overkill for simulating a human too, but the human is many times closer to that limit than the rock
This ties in with something I've been thinking about with regards to intelligence. A human and a similarly sized rock have comparable raw intellectual firepower, the difference is how they're organized