1992 Geo Tracker broken crankshaft

I had my car in for a water pump replacement, they also replaced the valve cover gasket and an O-ring on the distributor. The car ran fine, no timing issues whatsoever in over 2 years. The timing belt had been replaced approx. 20,000 miles prior by the same shop. 2 days later the car was towed back in (wouldn't start) they tightened up the distributor. 4 days later the car died and I had to have it towed back in again. They called me several hours later to inform me that the pin that holds the crankshaft & pulley together had sheared off and that I needed a new engine $3500 to $5000. I know that in replacing the water pump they had to remove the timing belt. Could having set the timing REALLY wrong or not seating or tightening things properly have caused the pin to shear off?