He's not just some dude that randomly sat down at a public piano at the mall. His name is Henri Herbert. He travels to public pianos all over the country and plays the same tune. Doesn't make it less impressive, but kinda takes away some of the essence of it. He's also in a band called The Jim Jones Revue that has a bunch of albums and videos on YouTube.
Edit: I found this out in about 5 minutes of digging. Never heard of this guy before.