I usually buy a Toffee Crisp and sometimes a bottle of water. I have never even considered that I may be stopped - but the cinema management is within its rights to refuse admission for this reason. i think the gentleman was unlucky being searched, but the response was legitimate, and he should either accept the policy, or view elsewhere.
If i was stopped, I woul accept the situation, hand over my goodies, and go in without them - I can manage for a couple of hours without chocolate.