Few of their stories involve humans eating other humans.
Sanae's ascension, Byakuren's peaches, Sakuya's leg and the frequent topic of wholesome human predation. It's gotten to be a running theme.
Byakuren doesn't eat the humans, she just uses them as fertilizer. Sakuya doesn't eat her own leg although she's curious about it (it's likely that was a joke though). Sanae I'll grant you since she was human at the time.
Cannibalism doesn't mean eating humans. It means humans eating humans (or any other creature eating its own species). Other things eating humans, even if they look passably human, isn't cannibalism.