For someone who hadn't really 'known' he could fly until about a month before, there's a definite ease with it as Trunks moves with her. Not necessarily graceful or elegant the way Celestia was, but his movements through the air were just as smooth. Even if his mind was trying to relearn, clearly somewhere inside, along with muscle-memory and body-motions, flight had been something he was very familiar with.

And without wings too. If Celestia is able to, she can probably figure out how he's doing so as well--it's not magic, although it could seem so. She's seen him use Chi-blasts before, but those are flashy compared to this.