First and foremost he isn't running 9s. Now that that is said for the 19th time, he got embarrassed by your system and tried to frantically save face in front of his girl by revving. Which with most girls probably scared the shit out of her. I doubt he got any *** that night.
If you would have revved back it would have gotten into a bigger shouting match and somone could've gotten hurt. You did the right thing by letting the little boy have his toy.