WhatsApp Delays Updated Privacy Policy After Confusing Users

I'll guess that Zuckerberg's definition of "private" is not at all the same as yours or mine. Personally I'd define "private messaging" to mean a way of talking with other people (via tech, obvs) such that nobody else knows anything about it - neither content nor metadata/network. But there's another possible definition, much looser, along the lines of "Having a conversation with somebody else" with no significant restrictions on eavesdropping or metadata collection - something closer to having a "private" conversation in an airport lounge: it's not intended to be heard by anyone other than the participants, but who knows who's listening in.