It is irrelevant whether or not you physically shorted the pin to ground.
Just touching the pin with a screwdriver held by yourself can produce a transient which can cause the PIC to reboot. I'm sure you have heard of ESD. Frankly, it is not wise to touch any semiconductor device with a metal screwdriver while under power.
Do you have a 0.1uF capacitor connected between Vdd and Vss, as close to the PIC as possible? If not, do so and disable the "Brown Out Detection?", whose purpose is to detect such transients and automatically reset the PIC.
How are you handling the Watchdog Timer?
BigDog