The right hand was set up by a jab, a jab which JDS used throughout the fight and Cain responded the same each time. JDS only had to throw it out there twice to read Cain and be sure that he'd do the same again, then capitalised on it perfectly.
That is called 'outclassed', not 'flash KO because it hit him behind the ear'. JDS knew the punch would land and he threw it with the intention of finishing the fight, Cain simply did not know that he was being read like a book.
You don't intentionally land shots to the back of the head unless you're cheating. That's where the shot hit Cain, to the back of the head. So which is it? Junior intentionally placed that shot behind the back of Cains head, or he accidentally hit him there? Given Juniors track record of being a clean fighter, it looks like he didn't mean to hit him in that spot at all.
Had that shot not hit him in that spot, I'm not sure Cain would have gone down at all.