If anyone is wondering what was up with the cooks reactions, here's my take:
Myne is actually putting them in an extremely difficult position. On one hand, she's acknowledged their skills which should be met with gratitude. On the other hand, she is a noble which means they cannot talk so casually to her, especially since she was talking to Benno and not them.
So what do they do? Ignore her comment and come off as rude? But then if they said thanks, they'd be talking directly to a noble, which is also a faux-pas in this world. Thankfully Benno gave them a way out and let them know "You're allowed to acknowledge her comments this time."
At least, that's how I picked up on it. In the light novel, I don't think they ever directly addressed what Myne did wrong. The courtesy rules of this world are pretty odd.