At least in southern California where I live, this is a pretty common thing among the sexes. Girls gravitate towards girls and are willing to open up and talk on a time, and the same goes for guys - that is how a lot of guys actually end up being friends; they happen to meet and chat out of the blue one day, and find they have a lot in common and become friends - then they'll introduce you to their friends and now you have a circle. I tend to cross gender barriers with this because I'm pretty gender fluid, so I actually found my group of current friends chatting up some girls in my art class about nerd comic book stuff when I noticed she had a Captain America jacket.
Just be cool with it - if a guy or girl starts to regularly chat with you, chances are you're actually blending pretty well. You'll know in a hurry if they are being flirty or not, but if a guy/girl just gives you a nod, a high, talks to you in a theater, or in a line, etc chances are they are just looking for a safe chat and you've managed to blend well enough to step into the circle. Celebrate!