Anything is possible. My hunch is that the guy just can't handle losing, and knowing that his opponent who admitted to cheating in the past beat him, it must be a conspiracy, right? If the guy hadn't cheated in the past it would still be a story but Magnus wouldn't have something to point to as a reason why he might have lost. In this case he has that benefit.
I'm happy to be wrong, either way I don't care, it's just the way I look at it. A big ego guy loses, can't handle it, crys foul, and the chess world goes nuts.
Its not exactly comparable but upsets happen all the time. Some of my favorites include...
Tyson losing to Douglas
US beating the Soviets in the 1980 Olympics
Nadal losing to Soldering in the 2009 French Open (that stung as a Nadal fan)
Any time the Maple Leafs lose in game 7 of the 1st round of the Stanley Cup Playoffs, yeah, fuck the Leafs