I know nothing more about this event than what I have seen posted here.
I value such videos, as a learning tool, that I prevent errors in the test flying I do. Part of the "learn from other's mistakes, you'll not live long enough to make them all yourself" spirit.
The video reminds me of the planning I have stuck by for those occasions where I have taken off in a "suspect" aircraft (I have never done any first flights of a new design).
I have at those "suspect" occasions, planned an aborted takeoff, and committed that no matter how well it seemed to fly, I would land back, for another go. Watching the video, it appears to me that there was a brief period, where a land back would have worked out. It would appear, that as a land back was not done, either it was not planned, or or it was, and the plan was not followed.
I once maintenance test flew a Cessna 206 which displayed tendancies similar, though obvioulsy less dramatic, to those seen on the video. After a very scary, and very short circuit, I reminded myself that even production aircraft should not be taken for granted, particularly following maintenance. There was no excuse for my not being prepared to land back on that flight. I should have been treating this aircraft as "suspect", but instead took it for granted, as I had flown it the previous month, and it was fine. I presume that all test flights should at least include a consideration of the need for a possible aboted takeoff.
I have no comment on the merits of the subject aircraft, but it appears to me that a test program stage, which might have increased the safety of the test flying, did not occur.
Perhaps more objective information, from which we can learn, will come to light in this unfortunate case.