A "stray" is an exile. He likely broke a law in the Lower Realms—usually by catching feelings for a human or refusing a contract. This makes him:
The Stray Incubus represents a unique fusion of high-tech corruption and demonic influence. Unlike traditional mythological demons, this entity thrives within digital networks, manipulating electronic signals and bio-mechanics to hunt its targets. Core Lore and Origins stray incubus guide