Pretty much. You say it's all mathematics, I'll say it's a simulation. Or maybe it's a dream. Or a the manifestation of another being's will. Or something completely incomprehensible.

Why should anyone care that it's mathematics? It's certainly not like any mathematics that we know; we can't do it some other way if we don't understand it. It's too big to fit in a brain, and too complex to simplify accurately. Since we don't understand its axioms, how do we know they form a mathematical structure?