Correct and it’s the same in many sports. Theres generally not “men’s golf” and “women’s golf” there’s just “golf” and “women’s golf.”
Women are not excluded from golf tournaments, but the requirements to compete (primarily how far one hits the ball) are vastly different. Thats why both play the same golf course, just from different tee boxes.
I think they're trying to say that if there was a mixed league it would always end up being 100% men at the highest level. Like, mixed league basketball would almost certainly be just men at the highest level because of how the sport works.
I sometimes play mixed vball rec leagues, the definition of a mixed league in our rec league here, says we "have to have at least 2 women playing at any time"
So maybe I think what they mean by "mixed league" is not a "Maybe Mixed League" but like "Definitely Mixed League" as in mixed participants being a strict requirement somehow?