I agree, but the article specifically says he used the "it's my cultrure" excuse. Not that it's relevant anyway, whatever your culture or religion is, you should follow the same rules as everybody else. I don't know the specifics either or how big or small the band was, it's just the principle that telling him to follow the rules that everyone else does, isn't any reason to blame the teacher.
But absolutely the department/principal should investigate thouroughly and get to the bottom of it all. As others have said, yes some teachers can be complete *******s and bullies (I've had a few of those myself), but kids can be absolute terrors as well especially if there's no discipline at home. What makes me wonder is the claim that this has been going on for 3 years. Why didn't they report the teacher to the department much sooner if he/she was such a monster? Of course this doesn't mean the teacher is innocent, it just means they need to look into it more.