The headmaster's reasoning is stupid - if we're going to take that biscuit comparison seriously, and say that the ingredients to biscuits can only be; flour, water, milk, sugar, salt, eggs, then the biscuits he gave the hero were heretical.
He is stunting biscuit making, and not allowing for such innovations as chocolate chips, or jam filled, etc.
Likewise to magic. If they're so concerned about possible damage done by unique magic, then they should be EVEN MORE involved in those magical innovations, and be secretive about them, not destroy them.
![pout :pout: :pout:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)