I see it a bit differently, see Cho as robotically performing either as brainwashed in Montgomery Clift style in “Manchurian Candidate” or in something more akin to demonic possession, as if he turned his soul over to the devil some time ago. Perhaps he opened his mind wide to let true evil trickle in, maybe with computer games. I don’t see authentic rage even when he tries to portray it, more of an obedience to an evil force. In his videos, he looks like an actor from Central Casting...
His responses sound inappropriate, to him, maybe not to a guiding force. It is as if he were a sleeper remaining invisible and unapproachable until the time for his role unfolded. Maybe he was being prepared by real terrorists from over a long time as a probe. Maybe he was being prepared by his father of lies.