To me the whole thing just raises a bunch of questions that don't have any satisfying answers.
Hiring more self taught and bootcamp people is often advocated as a way to increase diversity, and a lot of roles don't require a college degree (plus a lot of self taught and bootcamp folks are very good). However, on a large enough dataset, they will be weaker candidates. So if you use those sources to improve diversity, you'll end up with a correlation between diverse hires and more junior devs. Which screws up with every other metrics you'll look at.
Until the number of women in our field are on par with men, efforts to create an artificial balance will mean lowering the bar.
Bob's factory posts machinist ads on Craigslist. CL turns out to send Bob 90% males and 10% females. Bob decides to try to increase the number of females he hires, and advertises on a second site. Turns out this site is viewed by a higher percentage of females, and thus his number of female applicants increases, and the bar for hiring stays the same.
This assumption, on which your argument rests, is invalid.
I'm an engineering college student who's had conversations on this subject with admissions officers at my school. The gender ratio of accepted students is much more balanced than the gender ratio of applicants. Every year, the admissions department fields complaints from upset male applicants who were rejected; they feel that they were done a disservice because "the bar was higher" for them than for the female applicants. They point to the different acceptance rates for men and women as proof of this "lower bar" for women.
In reality, according to my school's admissions officers, the average female applicant is significantly stronger than the average male applicant. There exists, apparently, a huge volume of unqualified male applicants, who inflate that "80%" figure despite having no real chance at earning a position. We're talking SAT scores hundreds of points below the typical admitted student, no actual engineering experience, things like that. (I have heard that large companies like Texas Instruments also have this problem, which is why they place restrictions on which specific degrees applicants can have - to filter out that chaff.)
These men remain in the applicant pool where women would've washed out, the admissions officers at my school hypothesize, because it is easier for women to "give up" on STEM fields at the first sign of trouble due to social / societal pressures. Incompetent men, however, can think they're good at STEM more or less forever.
A more reasonable conclusion to draw, instead of "Facebook's male engineers are more skilled than their female engineers", would be the one that is presented in the article by the people who have the data. Namely, that this statistic arises from the confounding effect of seniority: Facebook's more senior engineers tend to be male, since the drive to hire more women has been more recent, and more senior engineers have code accepted more often.