Closer inspection time
Up + Down: Fluttershy's hooves are on up and down but also left, Twilight's hooves are on up and down
Right: Fluttershy's hooves are on right and down (possibly up too), Twilight's on right, but her back left hoof looks like it's on down but is actually more towards the middle of the pad
Left: Fluttershy's hooves are on right, down (partially) and left, Twilight is on what appears to be nothing, although it looks like she's on up if anything as the arrow comes along
Conclusion: Fluttershy is bad while Twilight is actually doing somewhat better, but that doesn't even matter because the game is rigged so that Fluttershy gets perfects while Twilight gets boos