It will be easy enough to tell. If the top longerons were pulled apart in tension and the bottom ones crushed together in compression then a bomb did not cause the tail section to depart. And it is possible to pull the elevators off without separating one or both wings, depending on structure, loading, and fuel load. I don't know why you say the tail section would be at a high velocity; it has a lot of "wetted" area and relatively little weight. I think it would have stabilized at a relatively low velocity after separation, which seems to be what the photo illustrates.