Yes ... it does. Read the definition ... it clearly says "intended to be fired from the shoulder" (or something pretty close thereto).
This is what you're looking for:
(7)The term “rifle” means a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of an explosive to fire only a single projectile through a rifled bore for each single pull of the trigger.
You're saying that "designed or redesigned, made or remade, and intended" also applies to the user, not just the manufacturer of either the weapon or stock and that your reading is so clear that anyone who doesn't come to your exact understanding needs adult supervision. I think you're full of it, and if I were inclined to be generous to you and the AFT I'd say that it is at best legally unclear and could be argued either way. That you want it to "hurt" for anyone who disagrees with your interpretation speaks ill of you.
So if I attach a wrist brace to an AR that has a short barrel, and I fire it one-handed with the brace strapped to my wrist as intended, I am within the law. If, on the other hand, I attach the same wrist brace to the same AR firearm with no intention of firing it one-handed, and all I ever do is shoot it like a rifle with the "wrist brace" lodged firmly on my shoulder ... I have broken the law.
If you own a braced pistol and have only ever used it strapped to your wrist, but when you let me shoot the gun I shoulder it and fire it have I manufactured an illegal SBR? When I hand it back to you is it now permanently an illegal SBR because I remade it, or changed intent somewhere? Or is it only illegal while I am holding it?
Or, again, if I have an unadorned AR buffer tube on a pistol and I fully intend to shove that against my shoulder while firing, have I manufactured an SBR? The only way you and the AFT can be consistent with your strained interpretation is to say that because I intend to use the buffer tube as a stock then by touching a buffer tube to my shoulder I have manufactured an SBR despite doing no redesigning or remaking of the weapon or any components on it.
If, on the other hand, the end use is not relevant then the SBR status hinges on the intent of the designer of the weapon and components. As the manufacturer of the pistol braces has stated their intent is for the braces to be used as braces, the misuse of their product does not change its design or intent.