Kay notices the wrecked car and asks what happened.

Tom politely answers that it was an accident but nobody got hurt...and quickly changes the subject back to Michael.

Not sure what else there is to 'get'.

Are you saying why was it added to the scene in the first place?

No answer really, except as with many scenes in The Godfather Trilogy - this extra detail adds a depth that would not otherwise have been there. After all, we do know that while Kay is busy writing letters to Michael, there is an all out war going on because of a double murder that he committed.

It is probably quite typical of what might be seen in the driveway of a powerful organized crime Family in the 1940's.

Apple