It probably means "flesh tones that our CV algorithms would flag as illicit" -- that is, they are probably prohibiting you from storing images that would create false positives.

To be honest, I think these clauses are broadly worded so they can suspend anyone's account and come up with a justification after the fact.

Note the prohibition of advocating pornography and expressing hatred.

Why don't they just put: "We can ban your account without prior notice for any reason we see fit."

Tons of services have that.

The explained what they meant by that. Non-human seems like a poor term though, perhaps "non-photo" would be closer to what they mean?

I assumed they meant, like, bare-breasted elfs. And presumably you can have a photo of a stallion with certain parts visible but can't have a similar painting of a centaur....

Either way it becomes very difficult to draw lines.