I don't think that roguecoder is saying that this was the issue. This is a perfectly valid decision, considering all the logistical realities and your stated goal. It colors the implied message that there was a 50% split in interest between men and women, which is what I get from the blog post(which I do realize that was not the intent).

Unfortunately, I think that the blog post is misidentifying the real success here. It wasn't that you got 50 women. Your signup strategy pretty much guaranteed this. The hackathon could have been an utter failure, but the original goal would have The real success is that not only did you have an even gender split, you still had a very successful hackathon. That alone takes more work than just throwing up the signup page and limiting the signups to ensure that the proper distribution is reached, and I think should be the takeaway here: That it doesn't matter whether it's a guy or a girl.