Bostrom himself isn't committed to simulation. His actual argument is that either we're almost certainly living in a simulation or the stated assumptions are wrong.

Moreover, there's a difference between "the universe is a simulation" in the sense used in the article and "my conscious experiences are a simulation." The latter is unconstrained by "number of qubits in the universe." The apparent complexity of this universe you think you're inhabiting isn't real, and neither is Scott Aaronson.