It sounds like an asymmetric situation was badly mishandled. More thrust on one side than the other, anyone with a multi engine rating knows what happens next. The cause could just as easily have been a real engine failure, the result was the same.
Six years ago TransAsia flight 235, an ATR72 crashed in Taiwan after the crew proved unable to control a twin on one engine. The regulator required all the operators pilots to undertake a test in the simulator in handling an engine failure, not all passed.