If you are not afraid of black people (that is a joke^^), you could look at him, and ask him a question.

Like who are you, why are you here, why are you smiling, or any other question that you prefer, with your own style.

If he wants to play he will probably mirror the question and keep smiling. (that is what I woud do^^)

anyway, you can't raise doubts if you don't try at least once to interact. The way I see it from where I stand..