Pinion bearing problem after transmission replacement

I WAS ON MY WAY TO HAVE MY 2005 GMC SAFARI VAN (127000 MILES) INSPECTED WHEN THE TRANSMISSION BROKE DOWN. I DROVE IT A BLOCK TO GET IT PARKED AND THEN TRIED TO BACK UP BUT COULDN'T. I HAD IT TOWED TO THE GARAGE WHERE THEY SAID THEY COULD GET A SALVAGE TRANSMISSION INSTALLED FOR $2500. I AGREED. ON THE WAY HOME AFTER THE REPAIR A FAIRLY LOUD WHINING SOUND EMERGED. I TOOK IT BACK AND AFTER SEVERAL TEST DRIVES AND PUTTING IT UP ON THE LIFT THEY SAID IT WAS A WORN PINION GEAR BEARING -- A VERY EXPENSIVE REPAIR.
MY QUESTION: WHICH IS MOST LIKELY: (A)THE DAMAGE OCCURRED AS PART OF THE TRANSMISSION BREAKDOWN & PARKING, (B) AS PART OF THE TRANSMISSION REPLACEMENT, (C) SOMEHOW COINCIDENTALLY AFTER THE REPAIR?