Question

The canterville ghost is a real story

Answer 1

Ghosts ain't real. They just don't exist.
so it's clear that "The canterville ghost" isn't a real story... :)

Answer 2

No it is an imaginary story written by Oscar wilde based on his imagination.It can be understood by the 2 incidents
i-when the ghost catches cold but in reality ghost do not catch cold.
ii-Ghost feels insulted when he is ignored by otis family but in reality ghost do not feel insulted.