It depends on the muzzel velocity. This is kinda the point of the articles cited...
The method of defining what is a firearm was simplified in 2000.
If it fires a shot or projectile over 500 FPS its a firearm regardless of what propels the projectile.
So overnight people who thought they owned airguns now owned firearms.. subject to registration.
You have to be careful about pulling up old documents. Things can change and they do.
Of course the police can't seem to keep up so no reason to think anyone else would.