So, I've been looking at videos trying to figure out what he was trying to do. Looks like he was flying low inverted, pushed over to almost vertical where he lost airspeed, and tried to pull into a 3/4 loop where he stalled at the bottom. Am I seeing that right?
No - the initial approach was upright, not inverted.
The manoeuvre wasn't a loop, as reported. What you see is a loaded roll that commences as the aircraft approaches the vertical, and changes the manoeuvre axis by 90 degrees. (The RAF has something similar, called a 'quarter clover', but we flew that with a more rapid unloaded roll in the vertical.). The problem with a loaded roll like this - particularly in a fast jet - is that it's easy to commit excessively nose-down for the available recovery height. That may have been the case here, but there could just as easily have been other factors we don't know about.
The flaps were partially extended, but that's not unexpected, as the Hunter has a combat flap setting which was commonly used for manoeuvring at lower speeds. I haven't seen anything that suggests engine failure, and in fact there's a high-res photo that shows a pronounced heat plume from the exhaust just prior to impact, consistent with the engine operating normally. In any case, I doubt that an engine failure after the top of the manoeuvre would've made much difference to the recovery height.
The jet certainly seems to be in a stalled or pre-stalled condition just prior to impact, with wing-rock and a high nose attitude, but to me that just looks like the pilot making a desperate and understandable attempt to pull out with max AOA, and doesn't necessarily indicate any mechanical failure.