This dude isn't the "real" Santa—but Kevin thinks that he's someone who's in touch with the real Santa, and can relay his message to the Big Man at the North Pole.
Fake Santa's wearing a fake beard, manning the seat at a fake Christmas village. At first, he seems a little rough around the edges—complaining about a parking ticket and telling Kevin:
SANTA: Make it quick. Santa's got a little get-together he's late for.
But when Kevin asks him to ask Santa to give him his entire family back, the guy softens up—probably because he's thinking Kevin's family died in some horrible way. He gives Kevin a bunch of Tic-Tacs, since the girl playing his worker elf took home all the candy canes. What a thoughtful gesture! Tic-Tacs are underrated.