Question- What was Vera's explanation for Mr. Nuttel's unusual behaviour?

The beauty of Vera's explanation of Framton Nuttel's unusual behavior is that it is so strange and exotic that it seems impossible that a girl her age confined to a country home in England could possibly have made it up. And yet it seems plausible. In a country like India where humans die of starvation on the streets every night and are carted away in the morning, there must be dogs who have an even harder time surviving. Dogs have a natural instinct to roam together, so homeless dogs would travel in packs and could be dangerous, especially if a person happened to be alone in an isolated place. Indians put up with a lot from animals because they do not believe in killing living creatures. There are some religious people who wear masks over their mouths to keep from accidentally swallowing an insect. And the toleration of monkeys is well known.

It seems almost necessary for Vera to tell her story about the pariah dogs at the end, since someone would naturally want to know why the visitor suddenly jumped up and went running out of the house without a word of thanks or goodbye. One of the three returning hunters has to say something in order to establish that they are living men and not ghosts. Vera's Uncle Sappleton asks:

"Who was that who bolted out as we came up?"

And Vera casually offers her explanation:

"I expect it was the spaniel," said the niece calmly; "he told me he had a horror of dogs. He was once hunted into a cemetery somewhere on the banks of the Ganges by a pack of pariah dogs, and had to spend the night in a newly dug grave with the creatures snarling and grinning and foaming just above him. Enough to make anyone lose their nerve."

The girl is bored. That is why she decides to stir up some excitement. "The devil finds work for idle hands." She must spend much of her time reading books. And since she is bored with her life, she probably favors escapist literature. She must have picked up the anecdote about the pariah dogs from a book about India. It really is a vivid picture, and it probably would explain how a man might develop "a horror of dogs."