In a charged moment in the novella, Equality 7-2521 breaks the rules of his society to tell Liberty 5-3000, a young woman he privately names the Golden One, that she is beautiful. In saying this, he is setting her apart as different from other people and communicating that he feels a special preference for her.
Liberty 5-3000's eyes show "triumph" when Equality 7-2521 says this to her. She then tells him he is "not one of our brothers, for we do not wish you to be." What she means is that she perceives he is different from the other males she knows. She wants to acknowledge and appreciate this fact. She does not "wish" him to be like everyone else, and she does not wish to pretend or treat him as if he is. The two recognize that they are special and don't belong in their society, where nobody is allowed to be an individual.