Sounds like he thought GFCI was fool proof. No shortage of fools, however.
Just about any do-it-yourself home electrical wiring book will tell you that the GFCI can’t do squat about the situation of simultaneously contacting hot and neutral while remaining isolated from a ground. Such a book will also advise of the importance of not allowing shock current, if it does flow, to pass near the heart. (So that if necessary to wire in a live panel, it is important to have insulating shoes or stand on an insulating pad not in water, and keep one hand behind one’s back.) If Kelley’s teaching didn’t even rise to the level of caution advised in a Home Depot manual, well he deserves some “static.”
Some folks are destined for Darwin awards it seems, and others work on multi-thousand volt equipment for decades and live to tell the tales to their great-grandchildren.