Spitfire said: Unless there's a wiring fault in the amp
That's what I'm trying to say,too.
The guitar's ground is grounded to the amp with the cable that you are using to play.
If the amp is not grounded to the mains earth then...maybe you will have a problem.
All commercial amps are safe.They have fuses (always use the same fuse as your guitar amp suggests) and are using plugs with ground.Of course you must use a socket with ground too.The socket that it is on your wall.
Maybe this person in his own studio has done some mods in his electronic gear without taking care of safety. 🙄
The problem was not cause his guitar was improperly grounded.His amp was too.
The high voltage came from his amp!This would happen even if the guitar was grounded too.
😡 Sorry if my english are bad.I can say more about this topic but my english don't help me.