I don't think that necessarily means that a site is sexist, especially a site like hubski with a very small community for what the site is.

Reddit is a much stronger case; reddit is very large and the majority of users are very immature and thus a great deal of 14 year old sexism is passed around which will naturally drive a portion of women away (though there is still a good segment of reddit that is female).

Since hubski is still in its very early stages in terms of population growth, the lack of women may just be something of a coincidence, the natural result of a small website which is not designed for casual use. Bear in mind, at least in the United States, women were not a large part of the internet until social media has really kicked off, and it is only with tumblr and pintrest that women have really started to hit deeper segments of the internet in the same force as men.

That being said, what we can conclude from the lack of women on hubski is that there is a lack of women on hubski. Without feedback from either dissatisfied users, random visitors, or members of the community, we cannot really draw conclusions regarding whether or not the ratio is due to sexism, lack of interesting content for the women who have visited, or just a lack of exposure. Or another reason entirely.