What proportion of the rest had accounts explicitly marked as male? My first thought is that most people of all genders probably get to that section of Preferences, go "Why would mediawiki want to know my gender in the first place? This is dumb" and skip it. Or they never fiddle with their preferences to that extent in the first place.
Keep in mind also that "identifies in preferences as female" is not a unified set with "is female", as you noted. Just glancing at a couple screens' worth of the log I see a handful of users who I know to be, or know probably are, female. So I'm hesitant to draw any gender-proportion conclusions from whether or not people ticked a somewhat obscure box.
This doesn't mean that female voters probably aren't very much in the minority in the election, but given what we already know about proportion of females on Wikipedia as a whole, that's entirely consistent with what expectations would be.