Inadvertent Whistle limit

[Loudwhistle]

A friend of mine was telling me a story that brought a question to mind that I will ask at the end of this:

First year JV boys coach is getting waxed by about 40 points in his first home game. A lot of his players have fouled out and there's about 20 seconds left to play in the game. He has four players left in the game and as his least experienced player #5 dribbles by his bench he loudly yells across the gym to him "Call Something" meaning call a play number out and then do it. He yelled coincidentally at his player just as the referee is going by so the official turns to the coach thinking he was the one that was yelled at and whacks him with a T! The reff signaled the T and everyone in the gym saw it, and when the coach tried to explain he was talking to his player the reff ignored him. Free throws were shot and the game finally ended. The coach really was yelling at his player according to information learned after the game. My question is at what point can a call be changed to an inadvertent whistle? The times I've gone with an inadvertent whistle is before I've communicated with the crowd what the infraction was. Thoughts?

Thanks