I think I am both, and they are simultaneously separate things and related things. The distinction between the two is that aromanticism is about lack of romantic attraction, and avoidant people might, say, have a crush on someone but choose not act on it, while an aro person would experience few/no crushes. So I think that's how you distinguish between the two. But it's likely that being aro reinforces avoidant tendencies, and would certainly add to existing confusion about what we're capable of doing or feeling.
I'll be sure to give you all the answers after I've solved all my problems in therapy lol