No you misunderstand.
It’s not documented by Twitch. We as third party developers are not supposed to be using it, or presenting the results/responses in this fashion.
It’s not using a library as libraries don’t tend to provide support for undocumented API calls. There isn’t a library to go get as the person whom made this page, potentially broke the Developer TOS to reverse engineer parts of the Twitch Website to find the call to get the data they are presenting.
If the documentation is not on Twitch Developer Documentation | Twitch Developers then it’s an API you are not supposed to be calling.