Dumb.
[1] His rescue of the Heroine and of the city would be known. A large share of the audience would be cheering for him.
[Addendum in Response to Later Comment: Most people wouldn't have witnessed the event in the first place, having fled or not been proximate in the first place. But those who did know — including the Heroine — generally had some reason to relate what they knew, and few if any of those who knew had reason not to report what they knew. In other words, the roar does not furnish a good explanation at this stage.]
[2] He knows that his hyper-competent teacher is perfectly sure that he will triumph.