I believe it happened. It has always happened. I looked like a boy as a kid and sometimes someone would say "hey sonny that's the ladies" and I'd say "I'm a girl" and they would look closer and say "sorry duck in you go". They never accused me of being a trans girl because, while obviously even then people knew some men or boys might believe they feel like "a girl", the idea that those males might believe they had the right to be in the ladies because of it was not on anyone's radar.
So to summarise:
A small number of women taken briefly as the opposite sex and challenged about it? Always happened.
A small number of women taken as being the opposite sex and accused of being an entitled transwoman is new, and it happens now and not then because the general public is now aware that transwomen feel entitled to appropriate seingle sex resources. The cat is well and truly out of the bag on that one.
But what I find both telling and damning is that TRAs and other gender-first posters are so full of concern that the increasing awareness that transwomen are using female single sex spaces might lead to the "collateral damage" of some natal women being mistaken for transwomen and suffering hurt feelings, yet utterly silent that accepting transwomen should have a right to female single sex spaces has already lead to the collateral damage of children and women being insulted, excluded and abused by trans women in women's spaces.
One might, might, almost wonder whether these TRAs and their allies are not in fact motivated by concern for women at all, but simply acting true to form in seeing women only when useful to trans politics.