I think he said what he meant. But, I think you meant "I know you linked a wiki that explains the film is based on a memoir in the first line, but you've already exposed yourself to the 'It was a book first!' attack, and I don't want to have to turn in my 'Ackchyually Guy,' membership card." Since we're speculating.
A more charitable reading would be that you simply meant, "Yes, that movie is based on a book by one of those marines." Maybe with some added opinion on whether you enjoyed it or found it equally as enlightening.
