I thought these new seats allowed the pilot to 'bang out' at zero feet and still live. Every days a lesson.
For instance, Flt Lt Simon Burgess (a Tornado GR1 PoW in GW1) was killed in 1996 when his Hawk T1 suffered a control linkage failure and rolled rapidly right on take off from RAF Valley. Although he initiated ejection almost immediately, the rapid rate of roll resulted him being ejected almost horizontally. As a result, the seat separation and parachute deployment sequence had not had time to complete and he was killed when he hit the ground still in his seat.
Loops are a basic component of Air Combat Manoeuvering even today. Conducted correctly using appropriate entry gates for speed and altitude, they are perfectly safe. Unfortunately, people are fallible and can screw those up, pull too much g, or even have an unidentified medical condition making them more susceptible to G-Loc.
We may never know for sure.