He did not "print a rifle", he printed what is known as a "stripped lower receiver," which is only a shell that holds the trigger assembly, magazine, grip, and provides a mount point for the buffer tube and two pin mounts for the upper receiver. The upper receiver and buffer tube/buffer spring are the objects which have the force primarily exerted on them.
In the eyes of the ATF he DID print a gun. The lower receiver is a 'gun' for the purposes of manufacturing. The upper receiver, buffer tube, trigger group, etc. are just parts...
I'm not sure what you're getting at. I think you're trying to be pedantic?
I said he didn't print a "rifle," you say "in the eyes of the ATF, he DID print a gun." I respond with, if you're being pedantic, he printed a "part which the BATFE classifies as a firearm requiring the stamping of a serial number should the manufacturer transfer it to any other individual." A part which, we all know, in and of its self is NOT a rifle.
