Probably, yes, it is her smile. But we are subconsciously processing everything else about you - your clothing and what it says about your sense of style, your priorities, your philosophy, your politics. The way you move and talk to people. How do you look at people?
It is amazing the volume of information we are constantly advertising about ourselves, and it only takes half a brain and a good guess to figure out, at least in part, what people are about and what matters to them.
A guy looks first at a womans body. He has her sized up but there is no complicating rating system in our heads, it's basically hot cool or ugly. But if a girl is at least cool, he goes and talks to her then if he agrees with you and/or likes your personality then he might start liking you. It's that simple. But I didn't include all the little details. Body type is a factor, some guys like skinny some guys like fat. Hope I answered your question.