What does 불여우 mean?

In the past, many Koreans had their given names, their adult names, and their pen names. For superstitious reasons, Koreans did not like using their given names outside their homes. In fact, in the past, Koreans were so secretive about their names that some Korean children did not even know the names of their mothers because people would usually refer to their mothers as "the mother of so-and-so," using the child's name in place of the "so-and-so." After Koreans reached adulthood, they were given adult names that their friends could use to refer to them without any problems, allowing them to avoid using their given names in public. Later, after Koreans had established themselves in society, many created pen names for themselves that described their character or something about them in some way. Many Koreans preferred pen names that were simple and humble. A grandiose or boastful pen name was considered boorish and unrefined. The following is my translation of a little story about a man who was embarrassed by his pen name. It comes from a book a have that is entitled, "하나를 배우면 열을 아는 이야기 어휘력 교실." The story is an example of Korean wordplay. "The Fox and the Red Fox (여우과 불여우)" In the past, men used adult names (자 字) and pen names (호 號) besides their original names (본 이름). After they got married, they were referred to by their adult names instead of their original names, and anyone could refer to them by their pen names. Once there was a man whose pen name was Yeo-u (여우 如愚), a good, humble name because its Chinese character meaning was dummy-like; but its pronunciation was the same as the animal name fox, so his friends were always teasing him about [being as sly as a fox], and he was always asking them not to call him by his pen name. One of the friends he asked answered him like this: “I’ll do as you wish. If the wish of a dead man can be granted, why not that of a living man? Apparently you do not care for your pen name, so if I do not call you by that, problem solved, right? Instead, you buy me a drink.” Another friend beside them chimed in, “Fine, then, but to suddenly not use it makes me sad, so I also will need to receive a drink before I can agree to it. And we will need to create a new pen name for you, one that will put our minds at ease. The friend with the pen name Yeo-u said that that was the best news he had ever heard, and they all went off together to the drinking house, ordered many drinks and snacks, and had a big feast. Soon the man with the pen name Yeo-u was drunk on alcohol, and so were both of his friends. The man with the pen name Yeo-u told them about all the unspeakable situations he had had to endure because of his pen name. His friends nodded their heads in sympathy as they listened to him. At the end of the party, as they were all standing to leave, one friend stepped forward and said, “So, from this moment forward, this friend of ours is not Yeo-u. Do you all understand?” The other friend answered like this: “Then, since his pen name is now not Yeo-u, we will add the character that means “not” (불 不) to his pen name and call him ‘불여우.’ That will be good, so from now on we will call him “Red Fox.”