Flukes are something that no one expects to happen ever again - f.e. that TK would beat Fedor in a rematch, that Takase would beat Anderson again. In instances that don't fit that part, they're often based on a "feeling", not on reality. They have little to do with reason, but a lot to do with emotion - flukes are rare upsets that have little to do with status or match-ups. They just "happen" on one night.
JDS' win wasn't a fluke. He stops people constantly and quickly, Cain gets hit a lot. Duffee/Russow is different, because the KO happened after a long domination and Russow isn't known for stopping people like JDS is.
All signs point to a Duffee victory in a rematch, where it's not clear to me who would win between Cain and JDS in a rubber match. Cain could've finished JDS in the first round, JDS was badly hurt and didn't get his wits back. Cain didn't recover in their first fight. If JDS wouldn't have, would you see the fight any different?