Well, it's biggest GUARANTEED payoff if anything.
Remember, Ken Jennings you could argue that his biggest payoff was only about $75,000. His was over 75 days, so that's DEFINITELY out for biggest single payoff.
Kevin Olmstead, you could argue, won a $1,000,000 + progressive. Plus, his win was not guaranteed, since he was still playing against the house.
In this UToC, barring all three players completely screwing up and scoring under 0, $2,000,000 is guaranteed.