According to Calvin Henry-Cotnam :
I once knew someone who had a pool pump on a GFCI and claimed that
every lightning storm his pool was "hit by lightning" because the GFCI
would trip. LOL -- if his pool was hit, his problem would be a lot
greater than just resetting the GFCI! The electrical storm was causing
transients on the power lines in the area that were the cause of the GFCI
tripping.

I suspect, rather than line transients, it was actually _ground_
transients inducing current in the line.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.