That’s an incredibly biased reading of that. It’s the gun + 14” of shoe string attached to the trigger enabling automatic fire that’s the machine gun not the string on its own.
Three years later, in 2007 the ATF decided differently, "Upon further review, we have determined that the string by itself is not a machinegun..."
https://everydaynodaysoff.com/2010/01/25/shoestring-machine-...