Hey, the guy in the chair is the one who suggested the punishment, according to the story. HE doesn’t feel bitter, apparently.
While arrogating punishment to the state is based, in part, on preventing private justice, it isn’t the only basis. The state has a duty to the population at large to prevent a recurrence of this guy attacking (bullying) innocent folks. Locking him away in prison is the best of the available options.
In short, the victim is entitled to express himself, but it is up to the prosecutor and the judge to meet out justice. And if I held either post, the guy would be taking a long term vacation to Starke.