A better question would be why open the two up - the ones he's already identified as semi-automatic, in order to show their similarity; but did not open up the third. Or why he subsequently felt the need to reinforce the lesson by showing how you could stick a semi-automatic receiver into something akin to a CQB stock. The answer is, of course, normalization of deviance. But hey, if you like your deviance without normalization; here he is being crazy on the internet. If he had said it outright, I wouldn't have used the word "implied." Instead, we have a few minutes of him alluding to the "fact" that the semi-auto AK variant is really no different than a hunting rifle; when I'm pretty sure it's obvious which of the semi-autos an infantryman would prefer to take into room to room combat.