I watched the video, but did not study the crash. Looked like the pilot expected to perform a high G pullout. And I'm guessing the airframe had other ideas. So my initial guess is pilot error on some level.
I just found a decent video. I’m going with 100% pilot error.
He went from a negative G push, to a roll, but during the roll, he was pulling back on the stick, loading the wing.
When a wing is loaded, that is when the wing is under high angle of attack and generating high, G, the roll rate is greatly reduced.
When you’re inverted, and the roll rate is reduced, your nose gets a lot farther below the horizon.
In an unloaded roll, your roll rate is much more rapid, and the nose doesn’t drop, so, your nose stays much closer to the horizon, you do not generate as much of a rate of decent, and the pull out is much simpler.
Less altitude is required for recovery after an unloaded roll, than after a loaded roll.
But when you’re low, the instinct is to pull back on the stick, and it appears that’s what happened, and it appears that loading slowed the roll rate enough that he couldn’t complete the maneuver with the altitude he had remaining.
All preliminary, of course, but the aircraft exhibited a very good roll rate in previous maneuvers. Unfortunately, during this maneuver, the roll rate was slow, which tells me he was rolling while pulling back.
So, pilot error.
