I'll take a shot
Sheer stupidity, Over-reaction, Fear of punishment, lack of common sense.
It's a simple case of a child with a sponsored free meal sharing some of it with a friend who is not sponsored. Evidently there is a rule that these free lunches cannot be shared by the student that initially receives it.
It sounds like the rule was put in place to prevent entitlement kids from selling their lunches and profitting at the sponsors expense. It would be difficult to prove that money changed hands.
Stupidity: The entitlement kid said up front he offered to share some of the meal free with the kid.
if that's true, the kid that received the shared food was not stealing. He may not have even known the meal was an entitlement meal with special rules.
Over-reaction: If any student is guilty of anything, it would be the entitlement kid for breaking a minor infraction about sharing a $3 free meal. Since the retail value was under $3, and this was a first offense, a simple discussion would have been appropriate. Calling the cops was ridiculously over-the-top.The administration (principal/viceprincipal) should have nipped this in the bud, unless the cafeteria workers went directly to the cops
Fear of litigation/punishment: It would not surprise me that the cafeteria NARC's followed the rules to the letter and felt they did no wrong. I suppose the cafeteria workers felt to not report something like that could result in their own dismissal or punishment. If the administration knew about this before the call was made to the police, they might have let the charges fly thinking if they get caught letting this kinda thing happen, it could result in the stoppage of the program.
What's seems clear to me is no one at the school used any common sense when applying the rules about entitlement meals.