I'm guessing that the spirit in the fire was distinguished from the spirit in the water for obvious reasons.
This is precisely an instinctive thing to have done. Why did man have to see a spirit in the fire or the water? Why not leave it at "it's hot" or "it's wet"?
You say that it's because the mind is dynamic. But in all the dynamic ways it could have concluded it had to be God (or gods, since we don't have a record of which came first).
Humans are very good at copying and combining concepts. The concept of animate invisible spirits/gods is a projection of our own sense of agency/self upon an unexplainable action. We then, as I said, imagine the spirit to be like what we are familiar with, a human form or animal.
Yet God isn't imperfect or incomplete like us. We look "up" to him. Even those primitives that inferred on fire and water saw spirits that did things that they themselves couldn't do as humans. The very notion that they ascribed these spirits human like characteristics to reduce their fear of them implies that the spirits were superior to humans in some way, which caused fear. They apparently had to be made more 'familiar', according to the theory.
For you, monotheism and black cat superstitions, are a result of a very long process. I can understand that. However, you also credit the initial thought that started the whole process as not being entirely original either. If that initial thought was also a result of a process, is there ever a true original idea or concept?