The fact is that the pilot didn't remove a flurescent orange "remove before flight" flag.
The guys who spotted it were just ordinary electrical engineers who didn't have to say or do anything, but the fact is, unlike some of the small minded respondants who frequent these pages, they are take a great deal of professional pride in everything they do and that includes speaking up for safety, even if they think there is the remotest chance they might be wrong.
I applaud them and so should you.
I know the pilot involved very well, he is highly competent and very experienced, his mistake was just that, a mistake - which any of you could make and probably have or will do in the future.
Those of you who criticise and/or make light of the actions of the guys who spotted his error are undoubtedly the unsafest people in aviation.