Go to the source page, zerohedge.com, and you'll see that the concern is about the group, Climate Feedback. Although I would agree that assessments of facts should not be so easily defended as opinion about said facts, it would be impossible for a fact checker to claim that all fact checking is not opinion. One has to assess the facts on a case-by-case basis and thereby corroborate and verify them with a number of people.

Most important is that we need fact checkers, even if they find what we may not want them to find. Climate Feedback has done an excellent job addressing disinformation, and right-wing organizations that don't like it have also created their own websites trying to promote their information, some of which are listed at /s/Shitpostnews, with ironic names like, Free Thought Project, Project Veritas, Proud American Site, TruNews, Anti-Empire, etc.

Note also that the link on the right side panel of this sub goes to a supposed "fake news checker" at the heavily biased zerohedge.com, and if you select it, you get a 404 page.

And now a word from Noam Chomsky regarding dishonesty and fraud: https://www.newyorker.com/news/q-and-a/noam-chomsky-believes-trump-is-the-worst-criminal-in-human-history