Perhaps women are less likely to be given the freedom to create the codebase (or part of it) and more likely to be involved in maintaining and extending it, and/or more likely to identify with such a role.
Another possible takeaway is if you want a clean codebase, you should hire a woman to write it, since women apparently care about clean code more.
Of course they do... whose house do you expect to be tidier, an average woman's or an average man's?
This is a go to point for me whenever I discuss how women in technology can make a substantial impact in the code base.
Have you ever seen a women's frat house?
I do not have anything to support it, but I think if you will be able to make such a study comparing women-into-programming vs men-into-programming there might be no difference in cleanness of one's house.