Hmm. Maybe the guy in the photo was a rat dealer, not a rat catcher. I just found this:

Mary Douglas (the mother of the rat fancy) once stated that Albino rats were introduced to great Britain by a traveling entertainer around the year 1800. In Victorian times, wild rats were caught in huge numbers for the “rat pits” that were popular at the time. Between the 1840s and 1860s some of these rats were kept, bred, and sold as pets. Pink-Eyed Whites were among them. In 1908 Beatrix Potter published her book “Samuel Whiskers” (a story about a wild rat and his wife). She dedicated it to the Albino rat which was a favorite pet when she was a child.