Yeah I'm not saying its right or women and men can't be friends. Just around here its assumed due to social norms. Like someone will tell a mom or dad with small children "go out with your girlfriends for a night" or "go do something with the guys"
And all it really means is " get out of the house and socialize"
Its a way of speaking that I think is common in some areas. If someone tells me "you are working too hard! Go riding with your girlfriends" they really just mean "go riding with whoever you feel like riding with but take some time off"
It IS the social norm where i live for people over a certain age to hang out in either single sex or couples groups unless its a specific activity like a band, group class, softball team etc.

Its maybe a good example of how sexism is so.ingrained in the fabric of US society that we barely notice it. At the same time like with heteronormative language for the most part I think.language just hasn't caught up.with how people actually think