"Most" does not seem to mean much here, while it probably is correct. According to the paper they only used thepiratebay as originating tracker. Right now the homepage lists 30 million peers. what.cd shows 9 million peers. I do not know how many peers Demonoid had, probably a similar or higher number. Some smaller trackers I checked all had around 100k peers. So just think of 60 smaller trackers like that and poof, the "most" is not true anymore.

This also only covers Bittorrent, not "most file-sharers".