It seems that this got way out of hand in the testing process.
They were testing the unit outdoors. Someone had either tripped over or kicked the grounding lead that was connected to the unit and did not re-connect it.
I don't think I'd like to be that guy somehow.
The fan on a VFD runs the same way (AFAIK) in both modes, it sucks air out, at least all then units I've seen do.
Hopefully this has been a learning experience for all concerned.
I still can't understand the lack of Equi-potential Bonding.