The only problem is that CT's world only has one moon. And it's never explained why it gained a second moon, so it lead me to believe that Harle's creation caused it to come into existance.
However, I like that idea of Lavos slamming into the moon. However, that also gives me another idea.
What if CT did have a second moon and Lavos did crash into it, but he instead obliterated it. That would explain why Azala said that "Soon fire shall rain down". Lavos was the only thing that crashed, but if he had crashed into the second moon and destroyed it, then that would explain why fire rained down.
But then that'd also give the possibility of Lavos landing in the Reptite Dimension.
Hence, we can always assume that the Dragonians simply engraved what they had learned from the humans in Fort Dragonia.