It's likely a factor but you're putting the cart before the horse.
Women have broken into countless so-called "boys clubs". Doctors, lawyers, marketing, etc... How is tech an exceptionally hostile environment towards women?
agpen is criticizing boys' clubs, a term that encapsulates a certain culture, behaviors, and set of beliefs. The gender of those participating in that culture is typically male, but women can and do perpetuate boys' club cultures on their own, often because that's the only way they can gain admission. It's fairer to see criticism of boys' clubs as a criticism of that culture and set of behaviors, and the idea that one must participate in those behaviors in order to be accepted, not of men in particular.
How is tech an exceptionally hostile environment towards women? http://geekfeminism.wikia.com/wiki/Timeline_of_incidents - Schneier links to this in the OP. If your response to that is "sexism happens everywhere," well, I'd like it to stop happening everywhere, and I'll start with my home turf.
What are these cultures, behaviors, and beliefs exactly?
To me, boy's club is another rhetorically nebulous term like patriarchy created by the girl's club. As long as we're speaking of generalizations, let me tell you about the girl's club. I used to date a girl that went to an all women's college. Every time I visited her in the dorms it was customary for everyone to yell out, "alert, man on board". When we ate at the cafeteria, five girls(FIVE), walked up to her and informed her there is no need for her to be dating a man. Without any consideration to my presence. Despite this unwelcoming atmosphere many were eager to inform me of the boy's club, patriarchy, and male privilege like they were reading a script of political talking points. These are women that are socialized to be hateful towards men and are blinded by this hate. They are socialized to feel like victims even though they go to a fancy school the average male couldn't afford.
Yes, there are gender centered problems that need to be addressed. But there is a lot of non-sense rhetorical noise out there created by the girl's club. It's like the girl who cried wolf.
The includes links to studies (like Sapna Cheryan, Andrew N. Meltzoff, Saenam Kim, Classrooms matter: The design of virtual classrooms influences gender disparities in computer science classes, Computers & Education, Volume 57, Issue 2, September 2011, Pages 1825-1835, ISSN 0360-1315,) that show a "lack of ambient belonging", that is being alienated by other group members, was the primary cause, and another that interacting with sexist male engineers lowered women's performance ( http://www2.psy.uq.edu.au/~billvh/LWSIvHB.JPSP.09.pdf)
Few people seem willing to accept that the lack of women in tech has something to do with men, but it does. Included the "high school girls" who aren't interested: the Girl Scout's study found that the biggest thing keeping them out was expecting to face sexism if they chose those professions.
This is not unrelated to how they're turned off further after and into their careers.