Theory

Just a theory of mine:

Guwon is indeed human—however—he might’ve been experimented on and he could also be infected before and somehow survived so he was used as a guinea pig for experiments and stuff until he becomes who he is?! He has some weird habits like not having the need to sleep, to eat, to rest, etc. He also has superhuman strengths, but has a lot of missing human emotions. The people in the “village” seem suspicious too and they for sure are not too fond of Guwon and are kind of scared of him; thinking that he may possibly be a walking time bomb.