I would remind all that GFCI's are not psychic and don't know the loads that they are sourcing. Is it possible that this gentleman was on a non-conductive ladder and not part of a fault path at all??? What if his wet tool let moisture in through cooling vents and got to the brushes??? If he was just a parralel current path to the motor, the GFCI wouldn't sense a differential current through its coil and cause a trip signal.
