During the course of this story, young Vera spins a remarkably imaginative tale, which later convinces their guest that he has just seen the ghosts of three men and a "little brown spaniel" returning after having been missing for three years. In fact, they are returning from a day's shooting and have not been missing at all. It stands to reason that if Vera's aunt had discovered her tall story, she may have been in considerable trouble.
Rather than having the sense to realize that he has been duped, Mr. Nuttel reacts in terror to the sight of the three men and dog, who he assumes to be ghosts. He doesn't stick around long enough for Vera to get into trouble. He turns tail and runs into the road so fast that he almost causes a collision with a passing cyclist. Of course, if there had been an accident, and the pieces of the puzzle were later put together in the correct fashion, Vera could have gotten into even more trouble, her lies being an indirect cause of the accident.
In a nutshell, Mr. Nuttel's terror causes him to run, rather than realize the truth, stay put, and tell Vera's aunt about the tall tales she has been telling. His gullible response to the incident spares Vera the tongue lashing she so richly deserves.