It is more complicated than that. The book is vague though colorful on many points, so there is considerable room for interpretation. On several points in the

It is more complicated than that. The book is vague though colorful on many points, so there is considerable room for interpretation. On several points in the book ornithopters are described as bug like, buzzing when active, and having bug like buzzing wings. The evocative version in the movie is consistent with one particular interpretation of what the book was depicting.