Hose and Peri
I agree that the circumstances of a mother and son may be questionable, however the provisional ball and meeting to determine the correct score at a later time is the correct decision no matter who is bowling. I've seen many bowlers turn and walk away after leaving a solid 8, 9, or 10 pin and then have the pin fall without them seeing it. I have covered the 4,6,7,10 split and never saw the ball hit any of the pins although I was fortunate enough to have someone else witness it. If no one actually saw what caused the pin to fall, we will never know exactly what happened. The only assumptions that can be made is that the rack knocked the pin down if there is a mutual agreement that the pin was moved far enough off spot so that the pin setter could not properly pick it up. Other than that, only a psychic could tell you what happened.
A provisional ball is allowed anytime there is a dispute over a foul, legal pinfall, or a dead ball and agreement cannot be reached by the two team captains or a tournament official. The protest is then referred to the league board of directors or the tournament management committee for a decision. If necessary, the matter can be be brought to the local association or ABC for a determination. (rule 10, ABC general playing rules)