Actually this is a pretty clear sign of a state sponsored attack, most attacks including the ones that the US does are not technically sophisticated but they are executed near flawlessly with a very good operational methodology, the other aspect of state sponsored attacks is protection; even the criminal elements of the security/hacking community stays out of military and government networks usually unless they have a pretty strong patron they can run to, no one wants to experience rendition or a drone strike both of which are very real threats hackers that attack government networks face.