Math is not really "knowledge of the universe" though, it's just the symbols and syntax we use to help map it when we try to understand the universe (through physics, chemistry, biology, etc.). Now, the maps that we have through maths can be extremely useful and very accurate to/representative of reality, certainly.
Ah yes solipsism, the principle that we cannot actually know... anything at all... beyond knowing that we ourself exist in some form because we are presently thinking about it, be it as an algorithm running in a simulation, or a brain in a jar being tortured with hallucinations on some 5th dimensional being's shelf.
I remember chuckling to myself upon learning that the answer to this situation is just don't think about it because it isn't productive.
Problem with that is It seems like a perfectly rational argument against the pursuit of productivity.
Btw, for those saying solipsism, yes, it is a thing but it's not represented here. Frank didn't say "this is my higher being's dream and you're all part of it", he said "we are all in a lower level of reality to that of the external Creator". It's closer to Abrahamic monotheism than solipsism! 😅