“..overpressure situation ..”
I suppose that’s possible, but it’s hard to imagine the tank would have no overpressure relief valve. It gets hot as hell out there, and I guess water is added and subtracted all the time, probably from a fairly large pipe. That just didn’t look like a ~~3 psi overpressure explosion to me.
No, that had to be a LOT of overpressure. I can’t see how striking an arc could trigger that, either.