There have been extremely butch women, lesbian and otherwise, since the 20s.
If and it's a fairly big if since this is only ever thrown around by TAs in the past couple of years, it happens at all, you know what?
It's happening because female people can no longer trust that male people are not entering their spaces. And they are voicing that they are uncomfortable, angry, that they do not consent. They now have to worry about who is who, because male people have created the situation where there's no trust in female spaces. This goes with the 'you probably won't know they're male' kind of argument - females never used to have to care what a female person looked like before males wanted what they wanted and took it without the faintest care or consideration for females.
The answer is not for females to give up, lay down and let male people and anyone who looks male do whatever floats their boat without conscience or consequences. Because that would be sexist batshittery, wouldn't it?
The answer is for males to respect females and their boundaries. Easy fix. If you're worried about butch women having a bad time then there's your answer!