Centre of Gravity, i.e. a cargo shift makes the sudden steep climb far more understandable. I read about a similar occurrence just after WW2 in India where a field gun broke loose and rolled aft destroying the aircraft's trim and ultimately causing the a/c to crash.
I do recognize the emergency climb to clear dangerous airspace, but my eyes though old are still attuned to what looks dangerously too steep. I'm not comparing model aircraft with the real thing, just that eyes which have learned to assess aircraft at a distance, whether smaller or larger, are well enoughschooled to recognize disaster when they see it..
Spitfires were found to have a very critical range of CofG, on the order of 16 inches of travel, and as they developed, and more and newer equipment was loaded on, the trim moved aft, resulting in a spate of unexplained disintegrations in the air. Finally, a Wing Commander who had spent time as a test pilot at Farnborough (the Royal Aircraft Establishment, the chief research airfield in Britain then as now) pulled out of a dive, and found the elevators so effective he was thrown forward far enough to be knocked senseless on the stick despite his straps, and to pop most of the rivets on the top surface of the wing. The good news was that he regained consciousness just as the aircraft stalled after a fairly long climb, and well clear of the ground so he was able to bring the aircraft home. Jeffrey Quill, Chief Test Pilot for Vickers Supermarine in the south, checked as many squadron aircraft as he could over the next weeks and found 90% of them to be dangerously out of trim. A very simple fix was found but loading and trimming instructions to the squadrons were made most emphatic. The further aft the CofG moves, the more sensitive the elevators appear to be, and the harder the aircraft is to control. Of course with a major cargo shift, there's ****** all you can do about it. Slamming the nose forward to straight and level, just won't work.
James, Your assessment too appears to be spot on, though I couldn't get a long enough view of the dash cam to make a reasonable asssessment. When the a/c appears on the dash cam, it's already in deep trouble, but I'm sure they simply didn't have either the time or sufficient strength to counteract the cargo shift. Damn shame..