Question: T on throw-in

[JoeT]

Situation:

Boys JV, NF rules. 4th quarter, tied game (not that it should matter).

A1 is inbounding the ball from his backcourt endline; team B is in full-court press. B1 is shadowing the ball at the throw-in spot. A1 releases the ball to pass onto the floor, B1 deflects it out of bounds.

Official calls T on B1, awards team A 2 shots and the ball. Official explains that B1 touched the ball (in the air) over the plane of the endline. (From my vantage, B1 touched the ball when it had legally crossed the plane, but that was the explanation).

My question: Is this a T (using the official's version) and, if not, what is it?

9-2-10 reads:

If an opponent(s) of the thrower reaches through the throw-in boundary-line plane and touches or dislodges the ball while in possession of the thrower or being passed to a teammate outside the boundary line (as in 7-5-7), a technical foul shall be charged to the offender. No warning for delay required.

In this case - even if the player "reached through the plane" and touched the ball, there is no dispute that it was no longer in possession of the thrower, so is it still a T?

Thanks in advance!