Here is my theory: he had no idea what they had done and there is no evidence to the contrary. ANY of us could have sold at $10 but we didn't. If we did, would we have been complicit in what NP and KK did? Of course not!
It is quite possible that only NP and KK knew of the deception, because if any other board members knew, they would have had a LEGAL duty to blow the whistle or they would be complicit too.