Does Kellhus have a peculiar blind spot where his father is concerned or was he just playing a part in Kyudea?
Kellhus', or any other Dunyain's, main weakness is that they often seem to lack the ability to see their own failings. The probability trance works on probabilities and statistics. Those statistics are only as good as the information they have, and on top of that they can still be wrong. Something with a 1% chance of occuring is dismissed in favor of the path that makes up other 99%, and most of the time they are right. However, when things go wrong, when the world conspires, when the gods interfere, or when dumb luck changes the outcomes, the Dunyain are left vulnerable.
I believe Kellhus might have failed to guess everything about his father, but his father failed as well, and didn't have enough time to backpedal to save himself. Moe is dead.