Aliens still live in our Universe with our physics. Are these aliens bigger than the solar system?
Maybe a different universe with different parameters could look m athematically different in major ways.
In a similar way, a set of different physics would apply to small enough aliens that are principally governed by quantum mechanics. They might never come up with the real numbers because they do not believe that quantities are dense.
We could think of more examples -- aliens who typically move at speeds close to the speed of light would have very different conceptions of time, etc.
Part of establishing communication is ensuring we're talking about the same things.
Therefore, once we've established communication, we'd be talking about the same things, such as what a flat plane is.
If you think humans are the only species capable of comprehending Euclidean geometry, say so, and defend the assertion.