The argument is actually right, if the retarded "bump stock is a machine gun" idea is correct.
If a bump stock is a machine gun, all semi-automatic guns are actually machine guns, since they can be bumped even without a stupid stock.
I've done it myself.
Problem is, a bump stock is not a machine gun and Trump's ban of them is moronic, illegal, and unconstitutional anyway. Along with the NFA, but that's another story.