I wouldn't worry...the parking pawl probably just didn't mesh with the parking gear teeth...typically this doesn't happen, as even a slight movement of the main or countershaft will allow it to drop in and lock the car in Park. But circumstances were just right and it didn't immediately find the notch in the parking gear. There is spring tension on it and eventually the car rocked a bit as someone got in or out or moved around and that popped the pawl into place....nothing to get concerned about....probably will never happen again.