Yes, Occam's razor.
Professors tend to hold controversial opinions. Random people will end up on the no-fly list. Sooner or later, that random person will be a professor with controversial opinions.
DHS does not use social media posts alone to place someone on watch lists, but they are incorporated into predictive assessments. Given two people who are otherwise equivalent, the one with public stated controvsial opinions IS more likely to end up on a no-fly list. By the govt's own admission.