Official called the right call and here is teh reason
a2 is in the FC when he jumps to catch the ball thrown in by A1 (regardless of where the throw in FC|BC"
as soon as A2 catches the ball you have PC/TC and the ball has FC status
When A2 lands in the BC he is considered to have been in FC and went to BC hence back court violation since PC/TC were established in the FC.
Good call by ref
