Sabato is weird in that he seems to really distrust polling as a source for his ratings, instead relying on personal hunches and guesswork.
Sabato's ratings have historically been quite good (though he overestimated Romney by quite a bit in 2012), but it seems with every update he picks a new basically safe race to declare as a potential sleeper, before taking it back with the next update. Before ID-GOV it was MN-SEN.
So Otter has as good a chance of winning as Kasich did pre-Fitzy scandals?
That chance of winning being, like, 5-10%? Sounds pretty reasonable to me.