It actually is true for mathematicians.
Most of us work in ZFC. Some people choose to work in constructive logic. Some people choose to only use countable choice. But we always know what logic we're working in and which theorems we can invoke. E.g. if you choose not to accept the axiom of choice you also have a sense of which results depend on Zorn's lemma and have to work around them. All of this is normal background for mathematicians.
So there's no need to allow the foundations of mathematics to vary unless you're working in logic and need to quantify over foundational systems or compare them. You would certainly never start a problem and then switch the logic midway through. That sort of thing wouldn't even be coherent.
You'd think I'd know what mathematics is about since I have a Ph.D. in it...
> fixed finite axiomatic system
ZFC is not a finite axiomatic system. nowhere did we specify that axiomatic systems have to be finite
> single...fixed
As I said above, there are people who study different logics. However the topic of conversation is individual problems. An individual problem does not switch logics mid stream and anyone working on a problem works in the context of a logic.
There's nothing wrong with taking an interest in a subject as an amateur. I thoroughly support it. But knowing what is taught in PhD departments and what mathematicians do is a precondition for understanding whether what AlphaEvolve is doing is similar to it.
If I wanted to know whether some AI tool was doing what humans do for, say, song writing, the first thing I'd do is figure out how song writing is taught, how professionals think about song writing, etc. And this is true regardless of the fact that I enjoy, support and often prefer outsider musicians.
This is true for programmers, it's not true for mathematicians. You can say programming is a subset of mathematics but mathematics is more than programming so proof search does not exhaust all the activities of a mathematician but it does exhaust all the activities of a programmer.