Earlier quoted context omitted.
This is absolutely the worst kind of analysis. Find some results we don't like, then work backwards using bogus inputs (that are easily refuted, as tzs did below, or which themselves may have been biased, faulty, outdated, not directly relevant, etc) and arbitrary math to determine, yep, the process was biased! I just proved it! Let's call out these bad people! There's no possibility that I am wrong, it has to be tho…
Either the ratio is around 250:1, or they got insanely unlucky, or the sample was biased. What's another possible explanation?
As other repliers have already stated: a) you chose a flawed survey to get your "10%" figure, b) the percentage of "women in open source" is far different, for a variety of reasons, than the percentage of women who are likely to submit a proposal to speak at a PHP conference in Germany, c) you dismiss any possibility that unusual ratios could possibly be due to reasons other than bias (is lung cancer biased because it overwhelmingly affects older people?)
You've offered zero fundamental evidence of bias (i.e. they filtered their mailing lists, they adjusted female speaker ratings, etc), other than the math doesn't work out the way you'd like, which isn't surprising given the invalid inputs and assumptions you started with.