Lying again?

The first day of school, I gave Sterling $20 to put in his school lunch account. Each day I pack Sterling a lunch. This consists of a sandwich or wrap, fruit, veggie and a granola bar. The lunch money is for milk, which costs .45 cents. From time to time, I ask him if I'm packing enough or would he like something different. We've make little tweaks based on these talks.
After two weeks, he tells me he's out of money. This didn't make sense to me. I asked if he was getting school lunches and he said no. I asked how much $$ was left in his account. He said one dollar. I gave him another twenty and marked it on my calendar in an attempt to keep track of where the money was going. Each day after school I would ask him what he spent money on. The reply was always the same. "Milk."
He came home one day a couple weeks ago and gave me the password to Edline. This is the schools way of tracking individual grades, fees, missing assignments AND lunch purchases. I went online and checked it out. Each day over the course of the one month he was in school there was either a breakfast, milk or lunch purchase...or all of the above. When he came home the questions began.
"What are these purchases?" I asked.
"I have no idea!" he exclaimed. "Wait...let me look at that." he continued.
I scrolled from day to day.
"Are you throwing away the lunches I make you?" I asked.
"No...I eat it." Said he.
"Are you giving your PIN to other kids and letting them eat on your account?"
"No...and when you give your PIN...your picture shows up so the lunch lady knows YOU are purchasing your own lunch...it's impossible to do that!"
Here is where I explained to Sterling that his account wasn't bottomless. This is also where I explained the only options of where the money was going were twofold.
1. You are eating school lunches/breakfasts
2. Someone else is eating off your account.
He had eliminated both of these options.
"Do you want to change your story?" I asked.
"No"
"I'll ask again. Do you...want...to change...your story."
"I have to go to the bathroom!"
In the bathroom, I thought he was trying to call a friend to get his story straight. He wasn't.
"OK dad...I may have had two lunches...but I really don't know what those other charges are...REALLY!"
"I asked if you wanted to change your story...you said no...you went to the bathroom, came back...and the story has changed for no reason...WOULD YOU LIKE TO CHANGE YOUR STORY."
He looked me dead in the eye for 5 seconds and told me no.
We continued to make eye contact...then he smiled.
"BUSTED! Where is the money going?" Here there is a 10 second pause.
"OK...I'm eating all of it and the lunches that you pack."
This is where we had the stern talk and now he only uses the money for milk. I asked if I was packing enough and he said yes. His story is...he is the first one in the lunch room and he eats my lunch waiting for his friends. When they arrive, he gets a school lunch. He has no story as to why he gets a breakfast. Yes...I feed him breakfast.
Lets recap what he was eating on any given day before I caught him.
Breakfast and milk at the house. Milk and breakfast at school. My lunch/milk then a school lunch. This is between the hours of 730 and 1230.
And yes...his "tell" has always been a smile. I hope he never plays poker as you cant win with a tell.