Boys always smile back at girls.

Men always smile back at women. There are several possibilities.

1, interested in this woman, want to attract the attention of girls.

I think this woman is good-looking, especially cute, and she smiles with appreciation.

3. I think this girl is very special and a little funny. Maybe someone else did something to her face or clothes. It's as simple as that

Of course, the best way is to ask him directly what you mean by smiling at me like this. He will explain it to you.