What exactly not necessarily true? Clearly CAA had enough circumstantial evidence to suspect gross pilot's incompetence and ask for pilots retraining, how many times in the past such decisive action was done so fast.
1) There is no evidence of gross pilot's incompetence. Only limited data has been released and certainly nothing anywhere near sufficient to
fully understand what happened to an experienced crew. There is, I suspect more to this than simply misidentification of a failed engine.
2) The Taiwanese regulator has NOT asked for retraining only checking.
The regulator had to be seen to do something for local consumption and they have reacted. (In the past this same authority has imposed sanctions such as restrictions on routes and new aircraft acquisitions).
This is somewhat strange as the majority of TNAs fleet are 72-500s which really is a very different aircraft and I doubt all their crews have had the delta course yet (or even if TNA operate a mixed fleet policy?)