Pre Match trial of outside area - observations

My son & I had 2 ticket checks yesterday. One coming in from the car park end which we expected, but another by the main entrance - what's the point of that?? The guy could see the direction we came from!
We bought 2 pizzas outside the ground which were a bit hot, so we thought we'd take them into the ground (East Stand entrance) to eat them - no chance! We had to eat them round the side of the ground standing up & then were let in.
The guy was apologetic and told us that they were the rules.
Apparently if I had made a pizza at home and brought that in, it would have been fine.
Any clarification of the rules would be appreciated! Surely the food was bought right outside the ground, so what's the issue?
 

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