The Doctor is confused. Not only because he's newly a pony, but because everypony seems to already know him. Especially a cute little filly that's the daughter of a pony with strange eyes. Derpy apparently already is his campanion, despite meeting her for the first time.
Yet while it's all new for the Doctor, for Dinky the situation is very different. To her he is no stranger, but a Stallion she is ever so glad to see again. The love of her mother's extremely long life. Also, Dinky has a plan. A plan to give her mommy and the Doctor something utterly priceless.