I watched the crash video several times and consulted with a friend who regularly flies a MiG-15 and F-86 at airshows....
The loop was started too low. Net result is the aircraft reached the apex too low. When the pilot realized that he may not have enough altitude, he dumped flaps and pulled hard on the elevators. This resulted in a nose high accelerated stall, (note that the Hunter dropped the left wing when it stalled) and the Hunter simply pancaked. Pilot error.
This is a common mistake, one most pilots only make once.
This video shows the stall very well....