officials error

[mdray]

From last year's refresher test: (I still don't get this one!)
A1 is awarded one free throw but the official erroneously tells the players that A1 will shoot two free throws. A1's first attempt is missed. A2 grabs the rebound and scores as the other players make no attempt to rebound the ball. After conferring, the officials count the basket. Were the officials correct? Answer key says NO. So what's the correct next step? Cancel the score and use the arrow?