Please, what happened here?

Being that she was only 16 there is no way to know if in fact she is gay/bi/straight for sure. Your idea is a possibility as are multiple others. She may have just been experimenting. She may be bi or gay. No way to know without finding out from her. Which is prob not an option. So I would do my best to get it out of my head, and if i honestly was losing sleep over it i would ask her. I mean you can find her on facebook or something i'm sure.