Fire regulations could be at the root of all this, though why the head didn't tell you is beyond me. Perhaps he was under huge stress that day and it was the straw that broke the camel's back. Even so,it seems very rude. A school play is meant to be very special event - and quite an emotional one.
Robinw, if the head has a real attitude problem, have you thought about contacting past members of the PTA - those whose children have now left the school, but have some years worth of experience here behind them - to see how they found him and if they discovered a way of handling him?