Before the false accusation arc, the beginning of a fight in the prison with one of the members of the cult that Onizuka attacked (and one of the main villains - later an ally - of the series) was being shown.
Until then, I didn't understand if the fight in the prison was in the original prison or in another one. Apparently, what was shown in flashback before Kai was in the prison to which Onizuka was transferred (and is being shown now). And where it seems that the plot will end definitively.
But I don't know, I have the feeling that this turned into a "plot hole". Because it's as if the fight had happened in the first prison.