These aren't the news, not by a long shot. Yes, there are some guys who put a female sign as their gender in order to troll some people, though is just for fun.
Most people do not care about the gender of other people, as it will not affect them directly in their normal interaction in the online forum. If a person chooses to use a female gender even when they are boys shouldn't concern you, as it isn't any of your business. They may be doing it because they want to be funny, they want to attract attention, or they are sexually oriented to the same ***. Either way they shouldn't be discriminated by your blunt ignorance.
Though I will have to disagree with you, 99% of NB aren't only boys. To be more precise, it will be over 50%, though not over 70%. You are forgetting about other variables such as females pretending to be guys or accounts without a gender. Some girls just decide to take this action in order to be less stalked by pre-teen predators who cannot find a girl in real life.
This isn't your business, and if you believe it is, is because you want to get involved with it for your own particular, twisted, superficial reasoning.
I recommend you to stop with this foolish act, though if you are one of those online trolls who think this kind of behavior is funny, then there is nothing it can be done. Though if you are one of those trolls, I would advice you to close your computer, go outside, and spend some time in something called real life.