The argument is that there exists a combination of states and tolerances when a P320 is loaded and cocked that could, theoretically, allow the striker to impact the primer forcefully without a complete and full trigger pull, one where you don't feel the break. This could either be while the finger is on the trigger (maybe a police officer pointing it at someone who has a weapon while commanding them to drop the weapon, for example) or not (in a holster).
Inserting that screw is meant to simulate a tolerance stacking issue wherein the pistol's components don't line up together in such a way as to prevent the striker from slipping past the sear.
Is it wonky? Of course. Could you probably do it with other pistols? Probably. Are there police officers and servicemen/women who need a convenient excuse for their negligent discharges? Yes. Should a real investigation occur? Also yes.
