I’m sure that sub in general was brought to his attention quite frequently, and I don’t see how that wouldn’t inevitably lead to him being made aware of his mod status. If for no other reason than simply that he would have likely had many occasions on which he needed to contact the moderators of it. Even if he mostly delegated that stuff, I just cannot believe he was completely unaware up until the moment it was banned.

You don’t really need to be fair to him; he deliberately allowed that sub to exist until it became too much of a liability to maintain it.