I discovered when reading Roger Ebert's review that this was not strictly filmed as it happened but that makes it a no less valid look at these people and their way of life.
The movie has been made in the same way that Robert Flaherty made such documentaries as "Nanook of the North," "Men of Aran" and "Louisiana Story." It uses real people in real places and essentially has them play themselves in a story inspired by their lives. That makes it a "narrative documentary," according to the filmmakers. A great many documentaries are closer to this model than their makers will admit; even "cinema verite" must pick and choose from the available footage and reflect a point of view.