To a narcissist, everything is about him.  So the question was not something to address with courtesy to the questioner, it was simply a vehicle for Justin to pontificate and prance in front of his subjects.  So of course he's surprised when he's called on it, he was caught off-guard when others saw it as simply a rudeness to the questioner (which it was, as well as an indicator of his character) instead of from his self-centered perspective.