He canted the weapon and saw the bolt fully to the rear. Solution; reload mag. IA complete. Logically speaking, there should be no way for a phantom round to mysteriously seat itself into the chamber. You would give the chamber a glance, nonetheless, 'cause you never know...
For those non-proficient with the firearm, I would definitely agree in taking more time to assess the stoppage and properly remedy it.
Anywho... Looks like a fun shorty subcarbine, but when it comes to the AR type I prefer mine in the 5mm range. If you really want some of the benefit of the 7.62 short, you'd be better off getting 5.56 rounds loaded with a heavier (80+) grain (and a barrel with a high twist rate). That's just my opinion, of course whereas I'm not taking into account the economic benefit of using the soviet surplus cartridge, rather just the performance.