He had the gun at the airport. That is pretty damning that he had possession or constructive possession.
Meckler had the gun in his possession while in the act of traveling when arrested at LaGuardia and is consequently protected by FOPA.
For constructive possession, it must be shown the gun was in new york state somewhere outside the federally protected umbrella, that Meckler knew it's whereabouts and could have accessed it.
So far, I don't see the gun placed anywhere in this case but at the airport.