Correctable error on bonus FTs

[CoachJW]

I'm a coach that likes to stay informed and knowledgable about the rules, so I read these boards often. I'll present a situation below, and please understand that I won't be reporting any officials to their supervisors or sending tapes to the state association. I'm just genuinely curious if my officials made the right call last night:

A1 is fouled on the ground by B1. Team foul #7 on Team B, so A1 goes to the line. Calling official reports the foul and signals 1-and-1 to the table. The other official lines up the players and signals "2 shots" before handing the ball to A1.

A1 misses the first shot. B2 jumps in and rebounds it while the other players stand and watch. The official that was underneath starts walking into the lane and blows a quiet "here, give me the ball" whistle. He beckons for the ball from B2, who hands it to him. Then the officials both realize the mistake and confer. The ruling was that A1 would get his second free throw, which he made. B3 inbounds the ball, clock starts, and game continues.

After reviewing the tape I honestly don't know what I would have done if I was in their shoes. I couldn't find anything in the 07-08 case book. These two officials are well-regarded by most coaches in our area and it was an isolated error, I just wondered if it was correctable or what the ruling would be next time it comes up. Thanks.