***I liked the movie, even though it wasn’t exactly true to the book. Movies almost never are.***
I read lots of books in my younger days and then saw the movies. Often the movie was NOTHING like the book.
THE PRIDE AND THE PASSION (1957 movie) is nothing like The GUN by C.s. Forester which the movie is based upon.
Same for SPARTACUS.
Often the movie producers would buy up the rights to a book and just use the name. Then they would write an adaption of their movie script for publication completely different from the original novel.
That’s true. This one was certainly closer than a lot of adaptations...which as you say shared only the title with the original!