My first response was not as precise as I might like. selecting as set of axioms is like selecting a large natural number. There are many so you need to use your brain to choose which to pick.

But notice some collections of axioms and theorems are more interesting than others, some have fruitful connection to our world, and some and interesting and complex inferential structure, while others are quite dull and provide very little value.

Notice this measure of value/interestingness is INDEPENDENT of the mind that selects the axioms and theorems. It is intrinsic to the structure of those axioms, and their connection (or lack of connection) to the world.

Thus our martian will have a very similar measure of interestingness. Their measure of interesting could differ if it connect to some purely social aspects of their society, which we do not share. But notice many of our social constructs ultimately ground out in aspects of the physical world. AND most great math does not tie to one aspect of the world, but to dozens and dozens of deep connections.

It is because of that rich structure, that it seems unlikely to me that a theorem deemed to be pivotal by our race, would not also be deemed pivotal to other races, for some subset of those dozens of reasons they happen to share.

The reason why I see the word 'discovered' instead of 'invented' is because I can choose to indicate theorem X or theorem Y. but I cannot change which of those theorems are intrinsically interesting. That interestingness is a fixed property.... and my goal is to consider math X, Y, and Z. Until I find an interesting one. (which I have then 'discovered') since it was intereesting before I found it. And in my finding, I did not change its interestingness.

(Ok, that was WAAAY to much to write, but I find the topic quite interesting... and I have never understood the mindset which says it is invented, yet I know it is a position that many smart people hold.)