Miles Using His Agency

I picked Miles up from school yesterday and we went throught the normal routine....how was school? What did you learn about today? I got all the normal answers as we drove to the park to play. Drew was asleep so I stayed in the car with him and started looking through Miles "Go Binder". He got a blue for his behavior and it sad that he is not doing his work. So after Miles wakes up we walk over to the park and I ask Miles why he got a blue. He says, "you weren't suppose to see that."
I said "I did, so why did you get your blue?"
"I am not going to tell you" he says.
"Do you know why you got a blue?"
"Yes"
"Do you know what you need to do so that you don't get one again?"
He looks at me and says, "I am not going to talk to you about this!" and off he runs.

Honestly, I starting laughing. What am I suppose to do? I thought it was funny that at 5 years old he is already choosing what we get to talk about. I asked him a couple more times about it, and each time I got the "I am not going to tell you." I am really wanting to call his teacher and get the story, but I have decided that I need to let Miles tell me what he wants me to know right now. Isn't that part of him learning to use his agency?