Interesting, what makes you so sure Celmomas was mistaken out of curiosity? The phrasing was pretty interpretive to me.
Its as interpretive as anything else.
I find it significant that his four horns are mentioned twice in a single passage. It draws needless attention to that attribute, and imo that's a hint to the reader.
Like I said, Celmomas is delerious, and I think this whole scene is from his perspective, right? Its not from the omnipotent third-person, nor is it Seswatha. Everthying we see and hear in this scene is interpreted through the lens of a dying Celmomas. He sees a God, and he sees what he thinks is his son. But what does the god say? Simply:
Behold the son of a hundred fathers
Behold the end of the world
We know how he interpreted this because of what he tells Seswatha: that his son will come and save the world. That's really the crux of my interpretation - that Celmomas was so out of it at this point that he misinterpreted "your son will destroy the world" as "your son will save the world". It's a pretty huge freudian slip, thus, the entirety of the scene is called into question.
Circle back to the horns, again pointed out to us twice, and I think that Ajokli is the God here, not Gilgaol.
Granted, that's a bit of a stretch. After looking back at it, the rest of the description could pretty well be what you would expect the God of War to be, and not so much the Trickster. Nubile virgins, fields of smoking burning dead, wreathed in flames - that sounds more like a god of war than a god of shadows, assasins, and trickery. More Thor than Loki.
And after all, if the vision IS of Ajokli, can we really take his word for it?
Hmmm. Good question. Maybe that's the point of Celmomas' confusion? He tricked the King into starting a prophecy that leads the world to its doom. Without the prophesy, Kellhus might not have been able to co-opt the Mandate, never gained the gnosis. He would have had to war with the Mandate to wrest control of the Three Seas from them, losing many schoolmen in the process, possibly setting him back decades. With the prophecy however, Kellhus walks conditioned ground.