9 players on the floor.

[The R]

Here is the play as it was described to me.

Boys HS JV
Warning horn sounds to signify end of timeout. T gives go ahead point to L who puts the ball in the play. After the ball becomes live L and A5 realize that there are only 9 players on the floor. The A5, who had been on the floor before the timeout, runs onto the floor from the bench during a live ball and joins into the action. A5 does not gain any specific advantage such as a snow bird or blind side steal.

Officials stop the game and charge A5 with a techincal foul.
Following the game 2 varsity officials ask what happened then say since there was no advantage when A5 ran onto the floor and they were a player before the timeout that it should have been a no call. They also said there was a play in the case book about this situation.

I can't seem to find it.
Thoughts and reactions?