I think I’ve spotted a mistake!

Hey doesn’t Hermione say in Deathly Hallows that you cannot produce food out of thin air? Yep she does!…But in Chamber of Secrets Prof. McGonagall does make food appear out of thin air. Harry and Ron are caught by Snape(after they crash into the whomping willow) and then he calls Dumbledore and McGonagall. Then there’s a bit of scolding and they decide to give Harry and Ron a detention. Then everyone returns to the feast and McGonagall says that Harry and Ron will eat in Snape’s office itself and suddenly a platter of sandwiches and a large jug of pumpkin juice appears on the table. The plate keeps refilling itself. Is McGonagall such a powerful witch that her magic is beyond fundamental laws of Transfiguration?