Russians seek answers to central Moscow GPS anomaly

This might be accomplished by something no more sophisticated than a repeater, they're cheap and readily available to provide GPS location inside buildings. Simply stick an antenna on the roof and the indoor transmitters will cause indoor devices to resolve the location of the roof antenna.

I wonder if the same principle could be used to pipe an authentic signal a few miles then amplify it sufficiently to be preferred by nearby devices

Or, knowing the Russian penchant for secrecy surrounding the locations of government buildings and installations, they may have decided to not even try. Kind of like the way that plat maps for Soviet cities were intentionally obfuscated so as to confuse intelligence agencies (and local drivers).