This was a totally avoidable accident. A ground run is just as capable of going wrong as a planned flight and should never be carried out without all the basic safety precautions as such.
In my RAF days, flying Support Helicopters there was a song:
There's a Wessex on the ground, on the ground
With its rotors going round, going round
It jumps up and down and shakes itself to bits
And gives its passenger the $hits, $hits, $hits.
Based on a true story.