This is the kind of thing we have to deal with in NJ, which nicely sums up the issues with NJ. As noted in the comments by BigHayden, “NJ firearms laws are the stuff of legends. Even the police don't know what is legal and what isn't.”
The article quoted a police officer who was fairly clearly making it up as he went along. NJ law does not distinguish between gas-driven and spring-driven weapons - 2C:39-1 f. emphasis mine
"Firearm" means any handgun, rifle, shotgun, machine gun, automatic or semi-automatic rifle, or any gun, device or instrument in the nature of a weapon from which may be fired or ejected any solid projectable ball, slug, pellet, missile or bullet, or any gas, vapor or other noxious thing, by means of a cartridge or shell or by the action of an explosive or the igniting of flammable or explosive substances. It shall also include, without limitation, any firearm which is in the nature of an air gun, spring gun or pistol or other weapon of a similar nature in which the propelling force is a spring, elastic band, carbon dioxide, compressed or other gas or vapor, air or compressed air, or is ignited by compressed air, and ejecting a bullet or missile smaller than three-eighths of an inch in diameter, with sufficient force to injure a person.
If a gas-propelled airsoft is a firearm, so is a spring-powered one (and under the “similar nature clause, an electric-drive one, I guess). They all seem to throw a plastic pellet at around 300 fps
Secondly, you can buy gas-propelled airsoft as well as spring-powered or electric over the counter without dealing with an FFL – I bought one at a sporting goods store that had spun off their FFL into a separate business; and I can go over to a paintball supply house on US 22 and buy as many gas-powered airsoft as I like (and, incidentally, some SERPA holsters to go with, right off a Blackhawk!-branded rack…)
So, a young man’s life is damaged (possibly ruined if they can get the charge to stick) over a pair of toys and a misinterpretation of the law.