A friend of mine works for one of those widmill manufacturing companies.
He told me that the mills have a control brake so that the mill stops at a given maximum speed to prevent exactly what we see on the video.
He knows about this case and what what failed was the mentioned brake and as there was no other safe way to stop the mill the company decided to let it go with the hope of not losing the mill if the wind speed decreased.
That's why the video exists, as they were expecting the whole thing, the technicians thought they could learn something from it.
Most problably the fact of blowing up has to do with a combination of centrifugal force and harmonics together