Research indicates that men do tend to project their interest onto the woman. If she's pretty, if he likes what she's wearing, they are more likely to assume that she likes him back. Then as you noted, if she's smiling and being friendly (even if that's because it's a part of her job), the whole dynamic ramps up even more. Unless she's hanging around you table a whole lot more than is necessary in order to facilitate your meal, she's probably just doing her job.

This was an excellent piece and much needed. My husband's dad used to flirt outrageously with waitresses, even in front of his wife and kids, and it was embarrassing for everyone - except him, apparently.