What does it mean after the second this man saw me his pupils dilated and his face lit up He just kept looking at me and smiling really big?

Well, it seems that he believes in love at first sight, at least that's how I interpret this. You could choose to let him shoo off or allow yourself to see what he's like, experiment etc., not doing something bad, no. I'm talking about seeing what kind of person he is. Who knows, it could turn into something great afterwards.