No, it's not the name of a character from Harry Potter or Dickens, nor is it anything to do with pigs or hogs. Hoggett is a sheep somewhat older than a lamb, but too young to be classified as mutton. In New Zealand they consider a sheep a hoggett if it's between one and two years old. In the United States hogget is an animal from one and a half to two and a half years old, but you will probably not find it here outside of a specialty butcher or local farm.
(Image credit: Red Meat Industry Forum)