That's a good point. I believe that page is the current info.
A quick search of the wiki for "locallib.php" suggests that these pages need updating to reflect current best practice:
https://docs.moodle.org/dev/lib.php
https://docs.moodle.org/dev/Libraries_Organization
https://docs.moodle.org/dev/NEWMODULE_Documentation
I'll do a quick update of these page while I'm at it, any improvements on what I write are welcome!