Specifically a controversial opinion precisely within his academic field at a time when the topic mattered the most. Authoritarian societies will let you freely

Specifically a controversial opinion precisely within his academic field at a time when the topic mattered the most. Authoritarian societies will let you freely say non-controversial things too. He is not just complaining about students but also the administration not acting to defend him. The article directly claims censorship occurred. Perhaps they mean self-censorship due to fear. It does still count, though perhaps some few isolated threats may seem a lot worse to the target than they seem to others (go figure).