So if the link to the NYT article is published on the extremist forum, and you job is to search for the extremists, you'd search for the NYT readers instead of the readers of the forum?

Your explanation has no sense, sorry.

What is an "extremist forum" exactly? Ars Technica?? That link was in the Ars Technica article.

Where does it say that's how they ended up in the filter?