Regardless of what the truth is for that one particular post, I can think of various reasons why a woman would favor the responses from other women over those from men. And not just on SW, but online in general.
1) The "woman" who posts is really a man, as you suggest.
2) The post is about something women experience, and the poster was looking for support from other women.
3) The men are making flirtatious comments when the post is not something about flirtation, sex or romance at all.
4) The men are "mansplaining" and the poster has gotten sick of it.
5) The men are not taking the post seriously and are making jokes, whereas the woman who replies actually gets what the poster means.
6) The poster is a woman, but she is on the site primarily to talk with other women, not just in that one post. This could be because she is a lesbian, or because she is straight and married and considers chatting with men online inappropriate, or because she has gotten sick and tired of male behavior on the internet, or whatever.
