Flirting can be fun. I know I am a shy person and sometimes when someone starts to flirt it brings me out of my shell. Doesn't always mean seriousness. I will say that if it makes you feel too uncomfortable then smile and walk away. A smile makes them feel good and you aren't slamming a door.

Your sense of well being is more than likely the cause. Holding your head high, smiling maybe laughing once in awhile at something. People notice body language. You maybe showing them "Hey I feel good about myself. I am confident and strong!!" These things are attractive to some.

Take it slow and have some fun with it. Sometimes just returning a smile for a "wow you look great today" is as good as anything you could say.