Again, lightning follows the lowest IMPEDANCE path to ground. It seems weird because typically the period of the pulse is short. One over gives a frequency usually of 2 MHz or so. At that point it's a RF (Radio) problem. So things that look like a low impedance at RF get fried and things that look capacitive or inductive don't. I suppose being a EE, RF engineer for many years, and a ham forever give you a different perspective. The typical number eight solid is good for draining off charge before a strike but isn't effective during a direct or nearby strike. The several inches thick copper strapping needed and extensive grounding needed is prohibitively expensive so it isn't used on normal houses because the statistical risk of being struck by lightning.... Well... Is like being struck by lightning...
Having said all that, the outlet looks like a cheap quality overloaded GFCI, the underwater stuff mostly likely wouldn't have provided even as good of a path as thd surface of the pool, and with that damage the inside of the house and neighbors would have issues.
I doubt highly the lightning hypothesis. The toner cartridge is an interesting theory...