"If the whistle did come from the crowd, they should have immediately stopped the game."
Why?
Stopping the play because a whistle comes from the crowd accomplishes what the misguided fan in the stands wanted.
IMO let that play continue, if the basket is made, hit your whistle, find security, tell them about the problem, let them handle it. Maybe even have the table make an announcement to the crowd with the resulting consequences. If it happens again, then I agree a "T"
would be an option, but ONLY as a last resort.