I'm not trying to defend your processor. It seems to be badly designed. Since it have a design that means a failure in the main program is likely to kill the watchdog too. Way better is a watchdog with a one-way trap function. If enabled, it will stay enabled. And without possibility to reconfigure.

A play with an ESD gun might deactivate a watchdog. But in my view, the main processor should be able to see if the watchdog is running.
A play with an ESD gun might lock up the processor core, or make the program do strange things. But in my view, the watchdog should be able to react and reboot.
An ESD incident that can upset both watchdog and processor core at the same time by affecting a single link in the chain, means the processor is bad.
An ESD incident that can upset both watchdog and processor core but requires the two functions to be individually "attacked", would indicate a processor that does all that you have a reason to expect. There are no perfect devices that can handle any random ESD event without the potential for something strange happening.