Yup, figured I'd hate them. He saves them all from complete annihilation and then they banish him? That's how you repay the child who saved your lives? Seriously fuck this clan.
While I agree, it might have been a decision to protect him, people can be irrational, and there is a non-zero chance he killed one of the kids, Seito might not have killed one and they were badly injured and the MC accidentally finished them off, I'm pretty sure he didn't, but the main issue is that all evidence and chance of their survival was reduced to zero by the MC. So no one knows exactly what happened the parents blaming him for killing their kid is well within reality. It's not impossible that one of the parents might have tried to hurt the kid, by "banishing" him they gave him a punishment to placate the people and to get him away from a dangerous situation, while unfortunate for the kid he would have been an outcast either way, at least this way he won't be bullied by others or worse happen to him