Catch 21
The 'tumbling' description reminds me strongly of an eyewitness to the Asiana SFO crash, who described the 777 as 'cartwheeling'. But when the video was closely examined, it became clear that the aircraft had reached a high level of bank and was turning/yawing accordingly. But to the eyewitness in real time, and perhaps shocked by what she was seeing, it was seemingly obvious that the aircraft was cartwheeling.
And that was in daylight.
Perhaps a high bank angle, as well as yaw, might have been part of the sequence of events with the helicopter? Seen at night, such a manoeuvre sequence could easily have been misinterpreted.
airsound