It's not about definitely dismissing any possibility.While it's possible that the woman could just be a guardian I'm not ready to dismiss the possibly of her being his actual mother just yet. Blood relations have become a thing outside of Kairi and her grandmother
It's just a heads up to not jump to definite conclusions so quickly.
From what I've read across several media many people are quick to treat issues still unverified already as if they're canon text-based facts which may just serve to drum up overblown expectations yet again.
It is the same with this woman being Skuld just because she has black hair in the roughly same style or the connection/relationship between Player and Xehanort treated as one thing while it can mean actually different things.
I dunno if that is a side effect of the quickness and impatience of Social Media, but on the other hand I do get deja-vu of the days where some theories went around which insisted that Roxas and Ventus have to be somehow the same person/character just because they share physical appearance.