He was probably generated from a dragon magic core from Lecan's world, using a long armed ape as a template for his creation/sealed form in this world . There's been a few different people who came from the same world as Lecan in the past. (examples: Eda's dad (deceased), and an old man adventurer "Skull-faced Ogre" Zoltan (still alive))
It's actually fairly easy to generate magic beings from magic cores from Lecan's world. Shira is given a magic core from a dragon from Lecan's world, and some time later she brings in a "mate" (named Eureka) for Jericho. She also uses a core to figure out what makes a demon different from a human in the view of Lecan's Life Sense in the first place by, in her own words, reviving that dragon in a weakened state. At one point Lecan leaves a dog monster magic stone (from his original world) next to an exploding type magic sword and comes back to find a puppy running around, which is adopted by Jericho. There's a PoV gaiden chapter from Jericho in which he thinks to himself that if he really wanted to, he could use his original strength. Fun bonus, Jericho thinks of Lecan as "clumsy and cute".