The funny thing is how in hindsight, as someone who helped raise over 20 kids growing up, Suo talks like a teen often dealing with younger kids. I've talked about the audacity of this child, being the youngest in the class and talking to his peers like he's the adult in the room, but it makes sense with new context.
The same way people can sort of identify teachers of young kids by the way they talk.
Both his teasing and encouragement come with a certain quality, the kind of manner to keep things light hearted and kind of fun, so even a correction doesn't feel like scolding. Which, of course, with kids his own age feels condescending, since that isn't how teens talk to each other.
Add the fact that he's a mediator for the adults. No wonder he hates childish adults if they're the reason he doesn't get a childhood, himself.
It would be really interesting if he fights the way he does because he's had to break up fights in the streets without hurting anyone, too.