Goldfish in my pond?

Question:

I have a very small pre-formed pond. probably 8 feet long, 6 feet wide and 18 inches deep. I have water plants and frogs. This year when I put some fresh water plants in the pond (water hyacinths and some kind of oxygenator) I ended up with fish!! I called the store where I got the plants and they said they were 99% sure they were gold fish. Well, they are dark slate grey with some black on the top. Are they really gold fish?? They don’t look anything like the pictures I have seen on the Web. Ideas?? I am moving them into an aquarium as my pond freezes to the bottom. I catch all the frogs and move them to a near by stream for the winter. I either cover the pond or dismantle it. thanks for any help you can give me. I have been feeding them gold fish flakes which they really like. Robin