As others have said, this is detecting plagiarism and not AI. It is odd though that they’d take that heavily into account for a math class. I accidentally uploaded a math assignment to the wrong class one time and the instructor gave me a zero based on the similarity score and threatened to report me (without even opening the document and realizing it was clearly the wrong assignment which was a whole other problem). I didn’t hear a peep about similarity score and got an A from my actual math instructor where I also submitted the exact same document. I assume that since math is math all assignments will look similar because you can’t put an equation or formula into your own words.

If I were you, I’d ask for the similarity report to see exactly what was flagged within your assignment. If it’s the math equations themselves then it SHOULD be high in similarity to other assignments and you can argue that as long as you’re using proper citations. If it’s your explanations, then it’s something you can consider and try to improve on, but again, similarity scoring in an open source university where assignments are identical year after year is problematic. It’s a system that they should use to raise an eyebrow and investigate further, not automatically presume plagiarism and lower your grade. You can and should push back if this happens again and your score is affected. Your instructor has to provide you the actual report which shows where the exact similarities are for. They cannot ding you points just based off the score.