Any reason why she would do this?

this girl im attracted to, were friends, weve never hung out by ourselves yet but we seem to talk alone when we always go out with our friends. well tonight seemed weird. i went to go sit by myself we were at a bar tonight, and she left our group of friends to come sit beside me and we flirted a bit and had quite a bit of a conversation. its always laughing, flirting and smiling between us. so then again when we went on the subway back home she came to sit right beside me and again we flirted and joked around. when we were all leaving to say goodbye, she said goodbye to every1 but me, then as she was opening the door to her car she said oh i forgot and ran to come and hug me. i dont understand, what was the reason for this and im hoping i can get some enlightenment on here. i got the wrong signals from this.