You stated that you “used to” get teased. I’m wondering how or why the teasing came to an end (good news). You also stated that you are “not bothered” by it (good news). In light of that, unless you ask someone who says something like that directly, you might never know for sure. I think if it’s in the past, does not bother you, and those people are not around to dialogue about it anyway, don’t invest energy in trying to make sense of it now.
I know you had to pick your battles, but if it happened in school, back then, you could have brought it to staff attention and said, " hey, not for nothing, but the kid said what I was doing is “so Asian” and while I don’t think people need to get in trouble…I want to know where he’s coming from." I would have used the school setting and staff as a forum to get a better understanding. Use the adults to mediate it. Whoever said that would have to think about what they said and why. That was your only shot at a real answer.
Those same kids tend to grow up and enter the workforce written up for hostile work environment or other nonsense. I think it is better for everyone’s sake that the schools catch it early on.
Glad it’s over.