Not Demons. There is a better way to perceive the story.

The aliens are clearly not THE aliens. They are Naked, ffs. They are nothing more than biological Drones. Grunts engineered to a purpose. A slave army used for raids to capture other species.

What would be a Great way to keep a slave army in check? Make them water soluble.

If they act up, give them the hose.

I don't know what he intended, or if he thought about it this much. But I prefer this idea to demons.