It doesn't claim that. You're conflating "women on GitHub vs men on github" with "a random sampling of men and women". Given that in the above study there seem

It doesn't claim that. You're conflating "women on GitHub vs men on github" with "a random sampling of men and women". Given that in the above study there seems to be dramatically fewer women than men contributing to GitHub, take the assumption that in the general population men and women have similar distributions of programming competence, and it seems women are more strongly selected against to contribute on GitHub than men. It seems reasonable that the women who push would have traits associated with greater competence. Thus men and women have equal ability, but women on GitHub can on average be more competent than men on GitHub.