IMO thats an extreme case where the manufacturer screwed up and didn't design into their rebuild a way to prevent FA restoration. Things like sear blocks, and different bolt or bolt carriers are used in lots of rifles to prevent full auto fire of the semi-auto versions, and it looks like nothing of that nature was done to those M14s.
You base that assertion upon....?
If you want to get down to it, it wouldn't take much time to turn about any AK back into a full auto weapon. Drill a couple holes, machine a slot in a rail, install the old trigger group, and maybe weld a tab on the bolt carrier. That thats any AK built on a new receiver even. Most all of them have things done to help make it difficult for restoration to full auto, but nothing is done for a full prevention.
They focused on whether it was originally a machinegun before being demilled.