Ethnography is based on fieldwork. In order for Chagnon to create this film about the Yanomamo people, he had to take part in their events he was observing, describing, and analyzing.
The ethnographic method requires direct involvement with the subjects being studied. For Chagnon to create this film about the Yanomamo people, he had to be an active participant in their lives, observing and recording key events while also analyzing the data he collected.