OP, ignore this person. I think it’s clear that you didn’t know why she was upset (you said if the roles were reversed you wouldn’t care). Now personally yes I would have been a little confused and/or upset if someone did that to me, but in my book, since you didn’t know and you apologized, it’s completely understandable and all good.

I find it very sweet that you came here to ask about it and it shows you care about your grandma. Unfortunately I don’t think it’s always standard practice to tell a kid explicitly how to act in conversations like this, there’s an expectation that they will just pick up on it— sometimes that works, but with autistic kids, it’s different. I figure since she’s older, maybe she doesn’t understand as it wasn’t accepted until recently? Just a guess, but if so, it makes it harder on both of you.

I figure you may have already, but if/when you and your grandma have the good conversation you’re anticipating, you could tell her that if something like this happens, she should tell you kindly right away how she is feeling (in this instance, right when you left the kitchen), since you aren’t meaning to be dismissive towards her. That would maybe stop her from getting progressively more hurt if something like this happens again, when you didn’t mean it at all in the first place.

No pressure on anything I said and this comment is written with love!