No, not really. You can tell a true story with a narrative film, or a documentary; what Herzog believes is that there is a truth beyond a strictly factual accounting, and he makes movies informed by this belief. There are a variety of techniques, but the most obvious is inserting himself into someone else's story, whether this is talking explicitly about the difficulties of making Cave Of Forgotten Dreams, or the scenes in Grizzly Man where he views Treadwell's death footage and then makes an in-camera judgement about showing it more widely; or basically all of Little Dieter Needs To Fly, wherein he takes Dengler back to Indochina and subjects him to much of the same suffering he experienced in his escape.

This also works in reverse, of course, notably with Fitzcarraldo, where he replicates an insane feat of human ingenuity that wasn't actually part of the real life Fitzcarrald's story.

In any event, all of Herzog's movies are worth viewing from my highly fan-boyish perspective.