That second link did not open for me at first, now it did:
That's absolutely dangerous, to do it that way; the illustrator had no glue what a thumbring looks like, even!!!! No figure shows a correct position of the thumb, either!
The first link shows a correct picture; the lip is to protect the tip of your thumb.
If you ever want to try: at least read Kay's book first, or better, go ask someone to show you how it works!