Kawhi Leonard smiles. He does. He smiled after the Spurs won the championship in 2014. He smiled as he was handed the NBA Finals MVP trophy. And the other day, he smiled when Manu Ginobili said something funny on the bench during a blowout. Do a Google search for "Kawhi Leonard smile" and click images to see a lot of pictures that show that if Kawhi is a robot, he's at least been programmed to smile on occasion.
But he doesn't smile much on the court, especially not after good plays, so there aren't a lot of opportunities for us to see the smile in its native habitat.