Mommy, they do it too!
No one should get a free pass. The word "gaff," to me, has an air of innocence about it...it implies more of an "oops" than an outright lie. When one calls himself a documentarian, he or she has to accept that there are limits on their exercise of artistic license. Intentional lies fall well outside that limit.
Besides, I'm not saying he should be drawn and quartered, I'm saying that serious lapses in judgement have cast a shadow of doubt over his own work. I think that's fairly well in perspective.