As Zoey says, but equally, someone could have tipped her off.
My wife very occasionally gets something similar, either because she's black, because she tends to look quite masculine or because she's has a large waist. She reckons these types are looking for a reaction, either fear or confrontation.
If they knew my wife, they'd know fear isn't in her repertoire. And after 35 years of mental health nursing, she knows about confrontation.
Just be careful love. These types are looking for trouble.
I strongly suspect, this woman was tipped off and was seeking to prove her toughness. It's a sad reality that many straight women today, having been beaten too often by some brute of a guy, tend to develop rather confrontational attitudes.