It doesn't make things fit, doesn't cause everything to click perfectly into place, does not cause everything Snack Service did (as revised according to Ione, the parts she knew) to make perfect sense.
...Sometimes you go with the wrong theory that is making some right predictions, if that theory suggests precautions you need to take right now before doing anything irreversible.
Keltham would, obviously, try to spare Abadar from the slaughter of the ancient gods, if that didn't come at great cost to mortals. But if you can extrapolate from the kind of story this is, it could definitely be the kind of story that requires him to kill Abadar, trading partner of Asmodeus. That sure is a kind of story that Keltham could be in, given how his life is going.
It's not certain, hardly. In fact it would be surprising if the story let him decode things correctly and that quickly, unless the character viewpoint has now shifted off him entirely and the rest of this story is about Carissa.
But sometimes you have to operate even a wrong theory that makes some right predictions, in order to avoid doing things that might be wrong and irreversible according to that theory.