Why does Mrs Pumphrey think the dog's recovery is "a triumph of surgery"?
Mrs Pumphrey thinks Tricki's recovery is a "triumph of surgery" because she is unaware of the actual treatment he received. Seeing Tricki's dramatic transformation from a listless, hugely fat dog to a healthy and active one, she assumes Mr. Herriot must have performed a miraculous surgical operation to cure him.
In reality, no surgery was performed. Mr. Herriot simply cured Tricki by putting him on a strict diet—giving him no food but plenty of water for two days—and allowing him to naturally play with the other household dogs, which restored his health and energy.
Explanation
Mrs Pumphrey is ignorant of the fact that Tricki's illness was caused by overfeeding and lack of exercise, not a disease requiring surgery. Mr. Herriot's 'surgery' was simply a strict regimen of fasting, hydration, and physical activity with the other dogs. Because she sees the dramatic, positive result without knowing the simple cause, she mistakenly attributes his recovery to a successful surgical procedure.