They might argue that Durham 3 were Public Figures, but that would fail because the Durham 3 did little to make themselves Public Figures. They didn’t want to be part of this, they didn’t run for office. Tehy became known through the uninvited actions of others.
Profs status as PFs does not protect them against litigation. It only protects someone who libeled or slandered them.
The point about the professors was that because of their position inside the halls of the University, and because they spoke, publicly ("ex cathedra" itself!) from a special standing as in such a position of authority, in a position to know more than the general public -- that an action against them for harms by false lights, or even defamation, could proceed more vigorously.