manually fact-checked by professional
journalists from BuzzFeed.
The article seems to accept -- uncritically -- "professional
journalists from BuzzFeed" as arbiters of fake news. Not a good start.That said, and anecdotally, style is often a fair heuristic for political agenda. It should be possible to improve the methodology of such research so it is insightful without such arbiters.
As an aside, it is not surprising that "that the style of left-wing and right-wing news have a lot more in common than any of the two have with the mainstream", for they often use the same, or similar tools to undermine society, a goal both have in common. They read the same literature about how do this, typically following a Lenisist approach.