IS this just HARMless flirting?

Just keep observing it and sees what happens, if it continues like this, then I would talk to him about it CALMLY. Just put some trust in your husband that he knows that he is married and that he would have enough common sense not to be cheating etc. Be calm about it, do not be paranoid. You do not want to cause extra unnecessary drama over nothing you know? And this is natural by the way. Expect some guys to be doing little things like that to other women, married or not.