Clarification on Backcourt Violation

[Jack]

Player A1 dribbles into the forecourt and terminates his dribble. Player B1 knocks the ball free and it rolls into the backcourt.
Player A1 retrieves the ball and is called for a backcourt violation.

The referee explained that even though B1 had touched the ball and knocked it loose - the referee saw the ball touch the leg of A1 after it was knocked loose and prior to going into the back court. Therefore it was a backcout violation.

Is this the correct call?