Meckler had the gun in his possession while in the act of traveling when arrested at LaGuardia and is consequently protected by FOPA.
You might try reading FOPA.
TITLE 18 > PART I > CHAPTER 44 > § 926A
§ 926A. INTERSTATE TRANSPORTATION OF FIREARMS
Notwithstanding any other provision of any law or any rule or regulation of a State or any political subdivision thereof, any person who is not otherwise prohibited by this chapter from transporting, shipping, or receiving a firearm shall be entitled to transport a firearm for any lawful purpose from any place where he may lawfully possess and carry such firearm to any other place where he may lawfully possess and carry such firearm if, during such transportation the firearm is unloaded, and neither the firearm nor any ammunition being transported is readily accessible or is directly accessible from the passenger compartment of such transporting vehicle: Provided, That in the case of a vehicle without a compartment separate from the driver’s compartment the firearm or ammunition shall be contained in a locked container other than the glove compartment or console.
It does NOT APPLY if possession of the gun in the starting AND ending state is not legal.
Without a NYC permit the gun is not legal to possess in NYC.