It's kind of annoying the website uses Classical Gas as his theme song, considering he was not the original writer or performer of the song. It's stealing credit in a way. I don't care if he covered it at some point (who hasn't?).
Not every song one plays has to be one they wrote or composed. I was surprised Campbell was as good on guitar as he was in the film. I know him so well for his vocals, I think they were trying to emphasize his guitar skills for those of us who were less aware of that side of him.