I don't think that's a fair characterization of what they're doing.

No? There’s literal billboards linked on this thread that say “what happens on your iPhone stays on your iPhone.”

Apple patting itself on the back.

I'm sure you know that the point of that billboard is to state that your iPhone protects your privacy. That is generally true, Apple is by far the most privacy-focused major phone and software company. Advertising isn't literal, if we're going to be pedantic here the photons emitted by your iPhone's screen technically leave your iPhone and definitely contain private information.

It's not pedantic to call out misleading advertising unless you're a shill for the ones doing the misleading.

If you one-way encrypt a value, and that value leaves the phone, with no way to recover the original value, then the original data never left the phone.