That’s a demon.
If he were undead, he’d have died on the spot and looked like the maggots too, but he looks perfectly fine and like a human. Especially because he literally doesn’t know ANYTHING except for violence with innocence not even a lab made guy would have. The natural disaster also gives off the same vibe, since usually, when natural disasters occur, a bad entity is what causes them (along with the undead) Guwon must have been sent down or up from hell and caused a disaster. That’s why people are afraid of him. To me, I think Guwon still has good intentions with mc since he’s never felt anything but the need to keep his duty and rules, so hopefully he stays good