The big sites were some of the hardest hit. For anyone who lost rank, how were your backlinks? If you had lots of article submissions, press releases, classified ads, etc all of those things were severely devalued and that could explain your drop in ranking. That's not really a false positive. If you've got good links that all kept their own rankings, however, then there was some kind of "false positive", I just have no idea how it would work.