As far as the Racist thing...
The two people in the photos do look the same.
Bill Mahar was more making fun of One Direction and Zayn Malik to the fact that we don't care, because he's just not that big of a star to care.

Context: I'm guessing that the reason he made the comparison is that rumor going around is that Zayn Malik quit One direction to join ISIS. In fact, it was even updated on his Wikipedia page by someone.

http://www.ibtimes.co.in/young-girls-promise-join-isis-bid-be-former-one-direction-star-zayn-maliks-wife-627408

This got Zayn's name in the news in many aspects, even though it was a hoax.
Several sites have run with the joke, which wasn't really funny to begin with.
http://islamicanews.com/report-zayn-malik-quit-one-direction-to-join-isis/

So Mayer's comment was just continuing the running joke that the media was already reporting.
Mayer's point was, "really, who cares?"