I don't think this Wikipedia page is describing the thing you think it is. Maybe it's the wrong link?

He's probably thinking about: https://en.wikipedia.org/wiki/Pingback

I think you're right.

It's a shame that this was so vulnerable to abuse. Webmentions as a concept is such a great idea. Maybe the more recent implementation is better, but it doesn't seem like many people (relatively speaking) are familiar with the idea.

Correct! Thanks for correcting