Will Ferrell is a lot more famous than Chad Smith is, especially outside the USA. Everybody knows who the Red Hot Chili Peppers are, but it's mostly bass player Flea and lead singer Anthony Kiedis who get all the attention. Smith, as the drummer, is largely ignored. That's sadly true of a lot of drummers in bands; it's the problem with being sat at the back of the stage! Because of the fame disparity, many people reading this are only now realizing that they've seen several pictures of Smith and believed they were actually looking at Ferrell.
Smith probably isn't a fan of the Christmas season, as we imagine people are constantly making 'Elf' references at him because they've got his identity wrong. He deals with the whole thing with good humor though. Ferrell and Smith even appeared on 'The Tonight Show' with Jimmy Fallon and had a drum-off. Needless to say, Ferrell didn't come away with the victory!