People given noble titles are allowed to choose their own preferred name. They might choose it based on a location or a family name or someone they admire or a military triumph of theirs (unless they're given an already existing title). In his case, that was simply the name he preferred. Other examples: in the case of King Edward VIII, he abdicated and was then as a courtesy given a title and the one he chose was the Duke of Windsor, named after the location of one of the favorite royal residences. In the case of Prince Edward, youngest son of Queen Elizabeth II, when he got married, he received a title, as is customary. He was made an earl and chose for his title the Earl of Wessex. There was no Earl of Wessex in existence though there had been one about 1000 years earlier. Prince Edward himself specifically chose that name based on the character of the fictional Lord of Wessex in the movie Shakespeare in Love.