Earlier quoted context omitted.
Aren't the AMP pages anyway delivered from the Google servers to the users? Then Google can track them anyway? I'm just a casual observer and that's just how I understood the idea.
AMP pages are served from the publisher's server as usual, but Google can easily direct their users to their cache instead of the official site. Every AMP page also includes JavaScript hosted by Google, so Google gets pinged every time someone visits an AMP page, even if it wasn't through their cache.
"Google products, including Google Search, serve valid AMP documents and their resources from the cache to provide a fast user experience across the mobile web."
So it's Google who does deliver from the cache. Moreover, they motivate others to do the same on the same page.