I have no idea how the classification of these work, but yes i was, atleast in my mind, referring to that glock since in the vid he sais it takes glock mags.

Well up to 50m, a well trained person with pistols has no problem emptying a pistol real quick with a spread of few cm. During practical shooting (im a member of the International Practical Shooting Club, i think ) some modified pistols fire so fast it is impossible to tell without physically seeing the pistol if it is single shot or full auto.

Personally my amateur opinion is that if it is originally designed to be shouldered, it's an smg. that popup pistol is still a pistol fitted inside a case. F*** if i know .

EDIT: Well we can also look at it this way that they are designed for different range. If one fits a pistol with a stock it wont give much range because the aiming mechanism of a pistol doesn't count in the bullet drop off trajectory, wheres an smg, which originates from a rifle is designed to combat at a longer range.