This obviously wasn't a drone for several reasons. One, no drone in production has 4 engines. A 4-engine drone would defeat its mission purpose, which is long loiter time and low fuel consumption. Drones have 1, or in the case of the new Euro drone by EADS, 2 engines.
Second, drones operating in U.S. airspace are required to use MODE C transponders. There are no exceptions to that rule, let alone when flying in Class B airspace. Doesn't matter if it has stealth features or not. No way the FAA would allow drones to fly stealth in controlled airspace let alone Class B around JFK. Any such drone operator would lose their license and military would even get in serious trouble.
This was either an RC plane or something like a Cirrus with a V-tail that was operating below Class Bravo and landing at one of the satellite airports (perhaps below JFK's tower coverage). But it was not a drone. No way. Since the pilot who observed it was from Italy, he is likely unaware of the production V-tail civilian planes we have over here and his only exposure to V-tails is through news media photos and video of drones he watches on layover in his hotel.
Finally, any person who flies a drone is either a pilot or, if not, heavily supervised by someone who is. The idea that a drone organization — private or government — that spends tens of millions of dollars flying drones in the NY Metro area would fly without a transponder through Class B restricted airspace around JFK is unthinkable. There's no way this level of breakdown could occur without severe consequences.
And the 4 engine reference clearly shows he's not correct. He probably saw a radio controlled B-29 that those RC club guys fly near JFK. The rounded nose would make it appear to be a drone. There are hundreds of people and several big flying clubs who fly RC planes on Long Island.