Just because you can't "see" it does not mean it's not happening and is a problem.
Have you never been discriminated against? Run up against a glass wall/ceiling? Denied promotion/raise due to gender, dress code, nepotism? Picked last in sports team? Never had siblings who know what to say to get you to react (to get in trouble for those actions)?
So, if your name is Joe (male) and I call you Pippy Longstockings (female) as you have kinky red hair, that's not a good book/movie reference?
Look, you are absolutely correct.
However, teasing is a different thing then insults and harassement and discrimination. And is benign (in the way it was used there).
The Knights Twitter could have compared the Bruins to.... say little baby Cubs. (Meaning they aren't ''Big Bad Bruins'' and are weaker. And that's fine. That's a joke, that's bravado. It's sports teasing. When people say ''Aaron Judge is the worst player of all time'', after he strikes out a lot, they dont mean it. It's teasing, it's fun.
Of course you'll say, teasing mustn't cross the line into harassement and real insults. And you are right if you say it can easily do so.
But it wasn't the case in my opinion here.
It boils down to this. When you use "you're a woman" as an insult to a man, you're saying that being a woman is worse than being a man. That's sexism.
Where was it said that a woman is straight up worst then a man? The implication of the joke was that a bunch of random women are physically weaker then some of the strongest male athletes on earth (a fact). And that's not the same as saying women are all around worst then men.
I mean, the Twitter could have easily compared the Bruins to a Garage League Hockey team!
Would that have been discrimination against Garage Hockey Players? NO!