This document documents official endpoints (green for POST, blue for GET).

It also documents "secret", unofficial, undocumented elsewhere and unsupported endpoints.

These "secret" endpoints were found by reverse-engineering Twitter.app for iOS.

I'd say this is a nice little cheatsheet. Which is useful at times, but I agree - this title is misleading.

Edit: The far right has a key, and just below is a box that has a few undocumented items.

Look at the colours - the grey ones are the undocumented endpoints.