Unintentional Batter-Runner Interference

 
With no outs and runner on third base (R3), the batter (B1) hits a long fly to right field. On the run, the right fielder make a great catch. R3 was tagging up on the play, so after the catch, the right fielder fires the ball toward home. However, his throw to home hits B1, who had rounded first base. R3 scores easily.
 
The defensive coach argues that a retired player (B1) interfered (even though unintentionally) with the throw and R3 should be out. What does the umpire do now?
 
Call
In the situation below, the run counts. B1 did not intentionally interfere with the throw. In addition, B1 was where he reasonably could expected to be (rounding first base on a hit to the outfield that could have gone for extra bases) and therefore was not trying to confuse the defense.