Yes, so if you were to encounter this butter in the wild, I understand that not seeing the label would throw you off. But in this particular case, in order to

Yes, so if you were to encounter this butter in the wild, I understand that not seeing the label would throw you off. But in this particular case, in order to comply with the instructions telling you to throw the butter away, you need to know that this is the butter you bought that actually contains milk but isn't labeled so. The very act of noticing that the butter doesn't have the right label tells you that it contains milk.