I have a German friend who works on large aircraft as an engineer. He once told me that he had been checked out to do ground runs, and I think he mentioned that he was checked out to taxi aircraft as well.
It's not rocket science, so that I don't see why an engineer should not be just as safe as a pilot when it comes to doing ground runs. Perhaps even safer, if the engineer routinely does ground runs when a typical pilot might only do one now and then.
It might be that there was a failure to chock the aircraft, something of that nature, that led to this accident. I guess we need to wait for the report to find out about that.