O contexto completo é (de Project Gutenburg ):
As I sit down to write here amidst the shadows of vine-leaves under the blue sky of southern Italy, it comes to me with a certain quality of astonishment that my participation in these amazing adventures of Mr. Cavor was, after all, the outcome of the purest accident. It might have been any one. I fell into these things at a time when I thought myself removed from the slightest possibility of disturbing experiences. I had gone to Lympne because I had imagined it the most uneventful place in the world. "Here, at any rate," said I, "I shall find peace and a chance to work!"
And this book is the sequel.
Uma definição secundária da palavra "sequela" é "um resultado, consequência ou inferência". O narrador é efetivamente dizendo “Eu tive uma aventura. Este livro é o resultado. ”