What?
George Lucas wrote the screenplay. He shared the screenplay with a ghost writer, Alan Dean Foster, who wrote a novelization of the screenplay. In parallel to the book being written, Lucas made the film. The book was published before the movie was released.
It’s really an interesting part of the Star Wars history, because Lucas made changes and rewrites during the filmmaking process, and Foster took some minor liberties while adapting the original screenplay. Foster also published his own sequel to A New Hope which had nothing to do with The Empire Strikes Back.
I don’t know what this title is supposed to be about, but it seems like they are trying to say that the movies are all based on a book, which isn’t true. Lucas did not consult with Foster about changes to the movie, and filming was mostly complete by the time the book was published.
Once again here to say I’m not saying the movie is based on the book. I, like you, just thought it was fascinating it turned out this way, and that we could wonder if the book is technically considered the beginning of Star Wars mania.
No, it isn’t, since the screenplay the book was based on existed before, and that’s what George used for the movie; his own screenplay, not a book written based on his screenplay.