It might be apart of the meme that most ponies are part food. You know the one I'm talking about, Rarity's made of Marshmallow, Rainbow Dash is made of Skittles, that one. Pinkie Pie is made of Cotton Candy. Maybe they think Fluttershy is butter due to her yellowish fur.It would certainly explain this: www.deviantart.com/art/Flutter… Which came out before this.... I checked.