It would be interesting to see the reasoning / prompts for this: I find it odd that it can solve it so quickly for such an open-ended problem with a large amount of text in an entire book.

The ciphertext is not just the end of a particular chapter, it is the epilogue of the entire book/text. So the deduction of it needing to use the 32 listed points (that happen to be on the preceding page [at least in re-prints on archive]) to decode - rather than anything else anywhere in the book - just strikes me as slightly strange? Almost as if maybe something [not in the text] tipped it off to this being the solution?