It's fiction. The story and characters in 'The Splendid and the Vile' are invented to entertain and engage the readers rather than being based on real-life happenings.
Synonym fiction refers to fictional works that play with synonyms. It might involve using many different words with similar meanings to create a rich and nuanced language in the story. For example, instead of just using the word 'happy', the author could use 'joyful', 'elated', 'gleeful' etc. throughout the text to add variety and depth to the description of a character's mood.