Read the following sentences from paragraph 5: "During the four years since his puppyhood he had lived the life of a sated aristocrat; he had a fine pride in himself, was even a trifle egotistical, as country gentlemen sometimes become because of their insular situation. But he had saved himself by not becoming a mere pampered house-dog. Hunting and kindred outdoor delights had kept down the fat and hardened his muscles; and to him, as to the cold-tubbing races, the love of water had been a tonic and a health preserver."
What does the narrator mean by stating that that Buck hadn't become a "mere pampered house-dog"?