I think if you accept a casual invitation, say for coffee or a movie, you can get an idea of why the boy is interested in you.
Perhaps you are more attractive that you realise - remember, when you look in a mirror, you don't see what other people see when they look at you.
During the course of the date, it is perfectly natural and acceptable to ask the boy why he asked you out, and see what he says.
Take it nice and slowly, and see how, and indeed if, things develop, but remember, one date is not promising a life-long commitment!