B) The study was cross-checked with a list of sites from a peer reviewed paper (H. Allcott, M. Gentzkow, Social media and fake news in the 2016 election. J. Econ. Perspect. 31, 211–236 (2017)) and according to the paper was similar.
There is some additional methodology in the study link.
The study appeared to correlate two sources to determine the nature of fake news:
A) The primary source was a list of fake news sites compiled by Buzzfeed Media: https://www.buzzfeednews.com/article/craigsilverman/viral-fa...
B) The study was cross-checked with a list of sites from a peer reviewed paper (H. Allcott, M. Gentzkow, Social media and fake news in the 2016 election. J. Econ. Perspect. 31, 211–236 (2017)) and according to the paper was similar.
There is some additional methodology in the study link.