They’re wrong that they rate the Guardian and Breitbart the same. First of all, they don’t have the same credibility rating. You also have to ignore the reports to reach that conclusion. Breitbart is a “Questionable Source.”
A questionable source exhibits one or more of the following: extreme bias, consistent promotion of propaganda/conspiracies, poor or no sourcing to credible information, a complete lack of transparency, and/or is fake news. Fake News is the deliberate attempt to publish hoaxes and/or disinformation for profit or influence. Sources listed in the Questionable Category may be very untrustworthy and should be fact-checked on a per-article basis. Sources on this list are not considered fake news unless specifically written in the reasoning section for that source.
The Guardian are not listed as a Questionable Source. They’ve linked to sources that have failed fact checks and failed numerous fact checks (mostly in Op-Ed), though 4 have recently dropped off the list in the last month or so (I think). Their fact-checking seems to have improved. They say this about them:
The Guardian holds a left-leaning editorial bias and sometimes relies on sources that have failed fact checks. Further, while The Guardian has failed several fact checks, they also produce an incredible amount of content; therefore, most stories are accurate, but the reader must beware, and hence why we assign them a Mixed rating for factual reporting.
‘Be aware that they publish an avalanche of great news but have failed a few fact checks’ is not nearly the same thing as ‘Questionable source that publishes propaganda and conspiracy theories! You must fact-check each article individually because they’re so unreliable.’ There’s no way you could read those pages and conclude those sources are the same. They say that Breitbart is clearly a much more biased and less reliable source (to borrow a phrase).