Well, my HV line experience is limited to a few operations on the 11kV distribution on a telecoms site, but the loud BANG! certainly reminds me of the first time I heard one of the 11kV breakers open. It was one of those "trolley" types, and boy did it make me jump when it released!

As for the guy who know more than you, I've had that all the time on normal domestic wiring. You end up wondering why he called you if he knows so much about it himself.... [Linked Image]