Look at how nervous he is in the video. He looks away because he feels guilty about lying. He also starts coughing. And he doesn't just say he doesn't believe it was a conspiracy; he actively downplays its importance, signaling to people that it isn't even worth looking into for themselves. That's what's so suspicious. He goes further than just censoring himself.

It's hard to say what exactly is going on regarding Assange. It's possible that he agreed not to treat 9/11, although that doesn't seem like him. On the other hand, the false allegations that forced him to remain in Ecuador's embassy for seven years and his consequent solitary confinement that may go on for years attest to the fact that the deep state sees him as an enemy, so it appears that there's a real component to him as well.