their base numbering system would be different than ours, their symbols for numbers would be different, their entire understanding of math and how to calculate stuff could be wildly different

The neat thing about math is it’s built upon universal truths that exist independently of how you describe them. 1+1=2 regardless of how you represent those numbers. Even among humans we have plenty of different ways of describing numbers.

Also, the best thing about science is that physics works the way it does regardless of how you describe it. An atom of hydrogen will always have the same spectral peaks, regardless of what units you describe those peaks in.

It’s these kinds of things we consider when trying to communicate with aliens. Take a look at:

https://en.wikipedia.org/wiki/Pioneer_plaque

https://en.wikipedia.org/wiki/Voyager_Golden_Record

https://en.wikipedia.org/wiki/Arecibo_message

These messages will probably never be received, even if there is intelligent life out there. But if something intelligent does find these messages, they will probably determine they are artificial, and hopefully manage to decode some of it.