True and even then they could be lying, Mumsnet may actually be 95% male posters, nobody will ever know for certain.
I know for certain.
The kind of conversation you see here, the responses ... the only way it could be 95% male posters is if 90% of posters tried very, very hard to pretend that they are women ... including doing intensive research on female anatomy, female socialisation, female life experience and feminism. Committing their whole lives to learning how women live. They would moreover have to believe that everyone else is female and the slightest mistake will expose them.
But no, not even then. Nowhere on a 95% male forum would there be talk about how the teen daughter handles her period, how the female friends handle their periods, how the poster herself handles her period ... nope. Just not possible.
The only not specifically declared female-exclusive forum where I have ever seen people talk about menstruations was a fanfic forum. 95% female users, approximately. Perhaps just 85%, but certainly the majority.
And on that forum, talk about feminism was met with a banhammer by the male admin and his handmaidens. So there is that.
I am on the feminist board of mumsnet, and I am very sure that at least 90% of people there are actually female.