Malichi (the accused) reported hearing somebody yelling racial slurs. But the school's allegations are about him joining the channel with abusive screen-names. One of his teachers says that it wasn't Malichi's voice yelling the slurs.
Malichi and an independent teacher both corroborated that there was someone shouting racial slurs, so by taking this side that actually the school is only going after the abusive screen names, are you saying that there were two separate people Zoom bombing this class, Malichi and someone else?
The school clearly knows they can't go after him for the racial slurs because he was on camera that whole time, so they chose not to focus on that. But it doesn't mean it didn't happen.