Supernovas create heavy atoms such as iron. Since it was freshly created material, any radioactive isotopes would still be hot compared to now, 2 million years later.
I guess. It's probably a little hyperbole. Iron-60, if it were highly radioactive, would have decayed to something else by now. Actually iron is about as stable an element as there is. The end result of the universe reaction when it goes to completion will be iron. Everything will be iron.