I wonder if he just does this at random.

I'm walking down the street in SOMA with the evening fog rolling in and I stop at a light behind a man. As we're both waiting to cross he turns to look behind him. Then he smiles like he's going to say something.
"Hey, could I ask you a question?" he asks.
"Sure."
"Think of a number between one and ten, and don't tell me what it is."
"Okay," I say and think of eight.
"Now let me guess, your number is seven. Am I right?"
"No, eight."
"Aren't you an optimist! You're that much closer to the number ten than I am."
I laugh.
"Are you an optimist?"
"Not really."
"Do you think optimistically?"
"Not really," I laugh.
"Well do me a favor."
"What?"
"Be optimistic. Can you do that for me?"
"Sure." He crosses the next street and leaves me at the bus stop, still laughing.