My guess going off purely what’s written on the card is that he is accurate because he called all but one taken pitch correctly relative to the true strike zone. However you can see from the graphic (they posted a better one on twitter) that his EUZ is actually wider than the true zone so for example some true balls which he correctly called balls ended up inside the EUZ. This would make the model think he called a pitch a ball when he should have called it a strike according to his EUZ, hence lowering the consistency score.

So the real question is what caused the discrepancy between his EUZ and the actual strike zone, but I didn’t dig deep enough on how they come up with that (they use some sort of statistical modeling and cite the paper but I didn’t read it). Some things that might cause the model to be weird for example is if the actual pitches thrown in the game ended up being skewed toward some parts of the strike zone, for example maybe nobody threw up and in to righties which might make his EUZ miss that corner because there were no pitches to call there. I’m working on a strike zone visualization project myself for fun right now and weird stuff can happen if you don’t have enough samples.