The reference included a direct quotation, and User:Lung salad had already quoted the relevant section over at Talk:Erich_von_Däniken#Ghostwritten. I'm not sure what your "foster father" line is about, as the documentary simply has the narrator asserting that the book was rewritten by a former science fiction author. The BFI link is clearly intended to give the reader further information about the documentary, rather than being presented as the entire source.
Either way, the assertion that the book was heavily rewritten before publication was made in Ronald Story's book, as I'd already said at Talk:Erich_von_Däniken#Ghostwritten. I'll restore it with a cite shortly.