To me filter implies an automated system. This sounds more like they are blocking specific sites after investigating them.

I'm willing to bet the wording was picked very carefully to split this exact hair.

Automated systems get their block lists from investigations.

And I bet parliament is full of invisible pink unicorns.

We can speculate all we want, but making up claims that are totally unsupported, and presenting them as actual statements made by a specific person in this way is pure character assassination.

I always wondered, if the unicorns are invisible, in what sense are they pink?

I think that's part of the point of their proverbial existence. Their description isn't self-consistent, which is just further emphasizing these are objects that don't exist.

But then they don't match the thing being compared with, which at least MAY exist.

That doesn't make it any better.

That may be so, but that does not mean the title is supported by the article at all.

I was thinking automatic filters that would block specific pages based on the output of some text analysis algorithm. This sounds more like a manually maintained blacklist, which would be very easy to work around using different users on social media and letting followers find you on Google.