The plates are all right side up. The main light is located off the right side of the scene. It casts a highlight on the right outside edge, and on the left edge of all internal edges. If one of the plates were upside down the highlights would appear on the opposite internal edges, but all of the highlights are the same.

Also the right edge of some of the plates casts a shadow inside of the dish. The edge of an upside down dish does not cause a self-shadow in the middle. Only concave shapes will do this.