It is not my position to comment on this unfortunate incident.
What I will say that the procedure in a very well disciplined company I worked for was to take the following precautions for any engine ground runs: Park brake applied, chocks in front of each MLG, aircraft pointed towards an “escape route” in case it jumped the chocks, a qualified person in the flightdeck command seat at all times, and, if necessary, a spotter to to keep a general eye on things.