Hm, that's interesting. For an ordinary playthrough (not speedrunning), I don't feel like Celeste puts much emphasis on maintaining speed. Almost the opposite, since you can stop really quickly on solid ground or by grabbing a wall. (Speedrunning is a different story because it uses techniques that you wouldn't use playing through normally.)
That said, the usual way to solve levels is to repeatedly figure out the sequence of moves you want to make to get to the next rest point, then make them in succession. Each move has some slack on it, but you do need to find a reasonable sequence. So if that's what "momentum platformer" means, that sounds accurate.