Like Bundy and Mitch themselves understood and both said, the last race was almost certain to come down to a "match race" between the two of them, and that’s exactly how it turned out. They were both prepared for it and the better sailer on the day won. If Mitch had (and he would sure as hell been trying) gotten the upper hand at the start then the results could have very easily gone the other way.
It's exactly the same for all the finals races of the Americas cup, except there are only the two boats out there on the water. As far as both Mitch and Bundy were concerned there was only the two of them out there on that last race as well. You could think of it also like a game of soccer where the two teams are tied nil all at the final siren, they then decide the results on penalty shots for goal. Some say that is unfair but most see the logic as “good for the game”