In the end, it was none of those. The Russians have now admitted that this unusual sight was due to a failed missile test just off the coast. A huge embarrassment to them. A 3 minute piece on this from the NBC Nightly News is embedded below. Near the end it notes that during the Cold War the Kremlin encouraged the belief in UFOs, so as to cover up secret military test flights and missile launches.
Well, so did the United States. ( And in the wake of the popularity of The X-Files a decade or so ago, that ended up boomeranging on the Air Force when huge swathes of the American public claimed to believe in the so-called "Roswell Incident," no matter how many detailed explanations were later offered by exasperated military spokesmen.)