It's not a virus or like typical zombie logic where you turn if you get bit. People die of natural causes or something else and turn to zombies.
I was thinking teach is like a carrier and guwon is a physical mutation. Like teach may carry it in his blood or saliva unknowingly, a different kind of mutation.
But also looking back the ring in the necklace is a collar which: dog. After Guwon was able to sleep, he started treating teach differently and after he stood up to Guwon the ring went on his finger. I don't know if it's because reach standing up instead of obeying makes him on par in Guwon's eyes or because he's also "weird".
I think you're right about the necklace and ring- especially when even Guwons is like "he's different from the others". IDK what Guwons is seeing that could possible make Teach the same as him lol I'm thinking his sleep walking and violence in those times might have something to do with it too.
I assume teaches violent sleepwalking is his subconscious screaming that Guwon is the danger and now having to fake loving a monster. He tries to cut off his entire hand, the one with the ring.
How he's the same could be a couple of ways, a viral mutation, Guwon slept for the first time for some reason. Or his willingness to challenge Guwon and not appease him like everyone else. His "hounds" are literally all yapping little puppies for his attention. No one challenges him, except teach.
Or are they affected by the virus differently. I've been wondering if teach's bad luck is more than just having to do with luck and we know Guwon isn't actually human... When he says like me are they both immune? Something's up. Whenever Guwon says something it never means what you initially think. Like the surprise is I killed your dad, but to him its I helped you regain your memories.