Back Court or Not

[BBallEvaluator]

A has the ball for throw-in along their endline underneath the basket. A1 throws the ball to A2 who is positioned above the 3 point arc. A2 receives the pass but muffs it and the ball deflects off his arm into the back court. A2 is the first person to retrieve the ball in the back court.

The official calls a back court violation and the coach whose team it was called on argues that possession was never established. The official explains to the coach that the ball legally contacted the Team A in A's frontcourt.

Is the coach correct since this is a throw-in and possession had not been established?