IMHO: That is an AMD-65 with the barrel hack sawed off back to the front sight base (the cut is uneven), then they removed the lower hand guard with the pistol grip and replaced it with a hand formed wooden one (the shape is lumpy looking, rough). The fresh black paint indicates it was built by a local smith to the customers specifications. Most that have been in the field have the "Battlefield Pickup" look.
The barrel was probably cut down short as possible for tight quarters battle and the lower hand guard mod for quick 30 round mag changes, the fresh paint is unusual as most of these customers don't want that newbie look.
The explosion: frame at .06 shows the rifle being fired in full auto mode with nothing unusual, frame at .07 shows a black piece of debris flying off to the left (the ejected shells fly to the right). This looks to be a linear piece of the front trunion from the lower left side, in the frame at .08 it shows the barrel blowing off the receiver and flying apart.
Why?
IMHO 1. The barrel pin was left out and the barrel moved forward as he fired the weapon (the area around where the barrel pin goes is light gray and may have not been inserted), the rifle is painted black and is usually painted after it completely assembled in this region. If the pin is missing the head spacing would increase with each shot fired until the head spacing reached a point where the back of the round blew off. Usually when this happens only the cover blows off, no the entire barrel assembly.
2. The gray area where the barrel pin goes had a barrel pin inserted after it was assembled and painted and when pressing in the pin may have caused the left side of the trunion to crack. Many builders press in the barrel pin from the right to the left, that could explain this.
Nevertheless, there was a catastrophic failure of the front trunion (the piece of debris flying off in frame .07) . Whether or not it resulted from a missing part (the pin missing), a damaged part caused by assembly error, or random catastrophic failure only "Root Cause And Failure Analysis" would/could answer this.
There are many ways to induce a cast as tropic failure, by treating the trunion with processes to make it as fragile as glass or merely cutting the trunion from the inside to weaken it. This however, is unlikely as the smith that built this rifle would no longer be building rifles when the shooter (the guy that crapped his pants) caught up with him.
There are many scenarios that may explain this occurrence however, this is merely my opinion and others are are welcomed to theirs.