Exactly! I'm sure I had a serious look on my face when she first saw me, but it was wrongly perceived to be RBF. I know how to intentionally signal, "Don't f--- with me" when I want a stranger to walk away. That wouldn't be RBF, that would be aggressive b*tch face.
I do think it was a judment she made based on the "totality of the circumstances" and not actual behavior. I believe that she thought me to be mean/b*tchy because of my outfit, posture, body language, and serious face.
We have presumptions about women that are unfair. If I had been wearing a T-shirt and jeans, and sprawled casually on a bench, I doubt she would have thought my serious demeanor signaled RBF.