There's a slightly contentious point when he says:
extras include three interesting short films about the tribes created by Schroeder to prepare for filming, all from 1971: "Le cochon aux patates douces," "Maquillages," and "Sing Sing." All of them focuses on various aspects of tribal life ranging from an unflinching depiction of food preparation with pigs (which highlights how odd BBFC standards really are) to dance and body paint routines.
It's not the BBFC that's responsible for animal cruelty guidelines, it's Stanley Baldwin's government for passing the 1937 Cinematograph Films (Animals) Act, which remains in force to this day. The BBFC has no choice, as it's compelled by the 1984 Video Recordings Act to take all relevant legislation into account when assessing films for home viewing - and I know from talking to an examiner that they hate having to do this, as artistic merit isn't a mitigating factor with the Animals Act in the way that it is with, say, the Obscene Publications Act.
So these apparently "odd standards" actually arise from the BBFC's determination to pass as much as possible in the face of a notoriously draconian piece of legislation. Handily, the phrase "if in connection with the production of the film any scene represented in the film was organised or directed in such a way as to involve the cruel infliction of pain or terror on any animal or the cruel goading of any animal to fury" offers two get-out clauses, namely:
1. if the animal cruelty was simulated;
2. if the animal cruelty, though genuine, would have happened regardless of the cameras' presence (since it wouldn't have been carried out "in connection with the production of the film").
Ethnographic documentaries are highly likely to fall into the second category, and that appears to have been the case here.