Absolutely, it could be that we are living in a simulation. It's just that there's no reason to believe that as yet. FWIW I think that a 'biological interpreter' is rather unlikely; it's probably just emergence from atomic interactions. (It could be planted there, however.)

The problem with your argument is that it makes too many assumptions. We know nothing about the nature of the simulator, nor do we have any reason to believe that (assuming we are not in a simulator) the universe works the way it does for any particular reason. Furthermore, the isomorphism you point out between the the physical world and computers are much more easily explained if you flip the causality chain: we are humans living in this world, and we modeled computers after ourselves and our surroundings.