Depends on the person, I'd guess. However, if I am for the sake of argument to accept your theory, my explanations would be as follows.
First one, that women don't always get taken seriously in "nerdy" domains. I didn't want to believe this at first, but unfortunately, there IS an attitude sometimes of "women don't know crap about technology." Thankfully, with anime and other gender-neutral nerdy activities, the numbers of female nerds are increasing, but still, there is some sexism, in some aspects of geekdom. Just like any smaller group that doesn't get taken seriously by the rest, it's easy to become resentful and want to prove oneself, sometimes in a snarky or not entirely pleasant manner.
The other theory is that, as many nerdy girls might have social awkwardness or outright AS as many nerdy guys do, bluntness and other stereotypically "unfeminine" behaviors might be more prevalent in geeky girls than in the general female population, and because this behavior flies in the face of expectations of what girls are supposed to be like, it's even more noticeable than in geeky guys.
In both cases, it seems stereotypes and expectations about gender cause more harm than good. Yet another reason to get rid of the damn categories already.