Apparently in addition to being almost flawlessly fluent in Mandarin, he can do regional dialects. "Dashan" means "big mountain," suggesting I guess a rural dude, the equivalent of "Billy Bob" or something like that. So I think the comedy is kind of character based, as in "what a character!" I guess.

So it would be like a Chinese-speaking guy coming here, as an adult, learning English well enough to pass for a native speaker, and THEN doing an impression of Boomhower. Or at least Hank Hill. Or for that matter, someone from remote Newfoundland. Or Chretien.