I have been away from academic anthropology for a couple of decades, but it wouldn't be too ridiculous to say that the social sciences tend to oscillate back and forth between materialist theoretical frameworks (like Marxism) and idealistic ones (which give culture / social practice more weight in explaining how people live, other than competition over resources). With occasional syntheses of the two. So in the context of Chagnon's career it was that he was annoying his mostly-Marxist colleagues (at the time) with his sociobiological explanations.