Flameouts can pop and bang but not like that unless the core of the turbine was breaking up.
Don't forget that the turbine engines of a very rapidly yawing aircraft can suffer a compressor surge or stall, due to airflow disturbances across the intake. A symptom of which is a popping noise.
Obviously, part of the AAIB investigation will look at the whole picture and part of that will be to check the fenestron tail rotor drive.