The ATF and other agencies like them will always want to regulate something in order to justify their continued employment with the tax payers.
In discussions with my friends, I've posed the following scenario.
Let's say someone is able to invent a "ray gun." You know; the type they use in science fiction movies. It does not hold any bullets or have a magazine. It dispenses a burst of energy rather than a bullet.
This hypothetical "ray gun" is very portable and can be carried in a holster or your pocket. Concealed carry laws aside, there is no federal or state law that I know of that would designate this hypothetical "ray gun" as a firearm because it does not dispense a bullet.
It's just like black powder weapons; muzzle-loading rifles, pistols, shotguns as well as cap & ball revolvers. Those are not firearms according to the ATF. Some states, on the other hand, regard black powder weapons as firearms.
If there ever comes a time when someone invents a personal defense weapon that uses a burst of energy to stop an attacker, watch for the apoplectic reaction and peeing of the pants from the anti-gunners.
In 1934 congress defined a machine gun but DJT ordered the ATF to designate a bump stock as a machine gun and ban it.
The ATF has also gone out of their way to take aim at Frankford Arsenal's reformation that is [by definition] neither a shotgun, pistol or rifle.
The article that the OP posted is spot on. The ATF has an attitude of arrogance when deciding who can or cannot possess a piece of metal or polymer.