Its funny that, even though poor ingredients were rigged for the rebels, the lackey examiners still have enough pride in cooking (apparently) to pass the dishes on the merit of them still being 'very good'. It goes back to vesting in the idea of evil chefs. If simply expelling these students were the end goal (and it is), simply lying about the quality of the food would be the simplest method to do so, as there is no read remediation against a subjective judgment. Eizen had the right idea; he gave it up too soon after it failed once.