I'm sure it was idle or just heavily lowered, but people dug around and found reports on old internet boards about time frame seeing him do it from the same timeframe and location.
If he never did it he pranked/lied about doing the prank and that is no better for credibility.
There is enough videos of F-18s doing 'push the throttle and bank' in a level flight on YouTube. It's fast, but it's not instantenious. And as an arm-chair pilot I can say what a multiton plane doesn't stay at the altitude with the engines at idle.
I find it very, very, very hard to believe that a fighter pilot would _shut down_ his engines in flight, at night, even more so if it's for a stunt.
Slightly more believable if he went to idle, and then full military power. Slightly.