Yes, that's what we're saying. They are not, in any case, natural science.
A mathematical proof is only valid in the context of some formal system, such as Euclidean geometry, some particular flavor of set theory, etc. For such formal systems, although we may not know all the properties (otherwise there wouldn't be theoretical mathematicians) we do know the essential rules, indeed we define them.
But science is the study of nature. We don't know the rules of nature in advance. Proof is therefore impossible with respect to postulates about the natural world. If it were possible then there would be no point in constructing, testing and investigating scientific theories in the first place. If we were able to do "natural proofs" it would mean we already had correct and final scientific theories. It would mean that we understood nature as a "formal system".
You could even say that claiming such "proof" is possible is blasphemy, as it would put us, insofar as understanding, in the same position as God, the author of the universe's "formal system".
IOW these mathematical systems are tools or instruments used in the process of doing science. But they are not science. Not natural science. They are of course part of the mathematical sciences. (Duh!)
Proof is therefore impossible with respect to postulates about the natural world.
Wow, that's far out.
So Newton's laws, Laws of Thermodynamics, Ohm's law and many other "LAWS" are not PROOFS OF THE NATURAL WORLD? Yet they all started as postulates and were proven mathematically.
I guess with such convoluted thinking about the difference between NATURAL SCIENCE and UN-NATURAL(?)SCIENCE, the proof of evolution as a fact is seen as absolute.
Good luck, Buddy.