Yes, desperation.
It's NOT a standard play at this juncture. Punt it deep. Let your D show its stuff, and play a little field position. Letting SoCal get even more pumped up by stopping you on 4th down and turn it over to the O with a short field in a game of emotion? Not a good call.
Shows cockiness, not desperation. Mack feels his offense can move against the UnpatrioticSCum.