No, far from it.
A man child is an adult behaving like a kid >on purpose< because they learned early on it works for them, especially if they don't get their way. Guwon has either been manipulated to be this way but deep down knew it wasn't right per instinct (the insomnia and throwing up as well as the beating himself and crying while smiling could be symptoms of that awareness) OR he forgot and was re-educated in messed up ways. Or he simply never learned what was ACTUALLY right.
It's similar, but not the same.
This is pretty much my thought. He's not morally well-informed, but because he's the town leader, people have to be unanimous in being immoral, like the vet-doctor's past, to not get on his bad side. But teacher is able to because of his title, more or less, I assume. And that lack of moral is really starting to weight on teacher.
So he’s practically a man child who has a lot of power and has never been told he’s wrong cause everyone else is scared of him?