Weird new behavior

I just got home from college and I was petting/ brushing my cat and she was loving it, rolling around and purring. She then started to smell my fingers before licking them. She then started with gentle nibbles on my fingers before biting down on my pinky all the sudden. It wasn't super hard, but I also pulled back. Her ears seemed fine and she was still purring/ asking for pets.
Is she just playing/grooming me or is this something to be worried about? She's never bitten me before and she's extremely gentle and loving/cuddly.