What's Up With Flirting?

Whenever I go to see this certain band that I am friends with, I notice one of the musicians, out of the corner of my eye, staring at me. I talk to him during breaks, we swap information about music, musical instruments, etc., and when he is on stage he seems to just zone in on me. Even if we are not talking during his break, I will sometimes feel eyes on me and look up and he is across the room, smiling at me! So my question is, if this is going on all night, would you say this is a flirtation that is just innocent or does he feel something more??? He has also bought me a drink or two in the past but I have done the same with him. We don't "hang out" at these clubs (he and I have our own separate group of friends) but there is mucho eye contact going on constantly!