What is the possible reason of having a note on my file that said declined to file charges from the DA’s office?

I was arrested in Delaware county Oklahoma. There were 3 of us in a vehicle not owned by me. I was a passenger. We got pulled over and searched. They charged us all three with possession of controlled substance and paraphernalia. Because the driver wouldn't claim it I was in jail 3 days and bonded out. The day before I had court I called the DA's office to check my charges and court date. The secretary said my file had a note on it from the DA that said declined to file charges. And I also found out that the girl driving also called DA and found out that she also found out her charges were also declined. Why do you think they would do that? I'm not complaining just curious.