Is it normal we dry hump when her roommate isn't around? is it sex?

I'm 19; my best friend is 20. We've only known each other about two months, but we're very affectionate. Most of our time is spent alone in her room, sort of canoodling in the dark, to the point I'm pretty sure that if her roommate isn't traumatized from walking in on us, she has to at least think we're dating.

Until recently, nothing was too out of the ordinary. My newfound best friend knew I liked her, and she liked me back, but neither of us were "ready" to pursue a relationship. As such, we've never kissed on the lips or anything like that. We just gradually became more and more affectionate as time went on. Eventually, it got to the point one would end up nibbling on necks and ears, and the other would sigh and squirm and let it go on -- encourage it, even.

That brings us up to now, where, when her roommate is conveniently absent, nibbling turns to biting, and cue some pretty insistent grinding and moaning from both parties, usually late at night. Last night, she didn't seem to realize she was doing it (she's rather innocent for 20, and I don't know if I should try and explain to her why her grinding against my leg feels like it does; she's a rather naive virgin), and we stopped and went to sleep, but this morning, the process started again, and she acknowledged it. When I tried to pull back because it wasn't intentional, she pulled me down again and didn't stop thrusting against my thigh until neither of us could move and she was a shuddering heap, clawing my back and kissing my neck alternately. I'm 99.9% sure she came.

Is this normal for two college age girls? Do you consider dry humping sex? Why or why not?