I teach aerodynamics amongst other things but it is difficult without the aid of flight data to say exactly what happened.

A similar thing happened to me some time ago flying a Rookie II, took me completely by surprise, it started rolling around it's velocity vector, (same position during a loop), but fortunately as I eased off the back stick it recovered in time. Maybe it was helped by being a delta with foreplanes and no gear down, I'm not sure but since then I have always given that area of the flight envelope plenty of respect and touch wood it's never happened to me since.

Rob.