I took this to mean: we can't legally guarantee your privacy for anything not on your own device; nobody can. Their claim seems to be that private data is kept

I took this to mean: we can't legally guarantee your privacy for anything not on your own device; nobody can. Their claim seems to be that private data is kept on the device (from https://www.apple.com/privacy/ https://www.apple.com/privacy/ ), and protected by encryption within the user's control. By designing the software such that private data stays on the device, it can't be gotten without targeted physical access (and perhaps coercing the user's passcode from them), rather than scooping up everyone's data from the cloud, unbeknownst to the users, and unauditable to security researchers. That said, I'm not sure how much trust I'd place in Apple, but at least this security model is to some extent auditable.