Experience
I agree that there have been a number recently where it would appear that an 'aero' has gone sour. A few years ago, I was at the top of a loop in a Chipmunk, about 5000', thankfully, when it 'flicked'. I scared myself senseless, however, I came away from the incident realising that I required to be 'professionally' trained - I had been self taught up to that point. In other words I did not know the recovery procedures.
That was what I did - I went and re-trained, however, the incident stuck. i.e. I never wanted to get into that position ever again, where I was not prepared.
I do hope that the other individual involved survives this, and sorry about the person who sadly did not.
I have made no assumptions about the training standard, or experiences of those involved.