If you are ? by police and are told you are free to go. You prove no knowledge of the crime 7yrs later u get state probation w/No arrest is it leagal

I was working and let a friend help. My pressure washer broke told him we would have to wait. Said his dad had on took him to the house didn't pull in or get out. He went on the house said he asked and brought the pressure washer. When we were done I serviced the pressure washer offered 50$ for letting us use it his father said it was stolen.. He called police I told them what happen they heard the guy on speaker phone admit he took it witnesses saying I did not pull in drive way or get out. They let me go this was 2010. We had one court date the owner first came in my behalf his son did not show. The officers came in my behalf. I left thinking it was over. Two weeks ago I had to go back to court and received state probation 6 months super. A year and a half in supervised. How could this happen. The guy who took it got 30 days for a FTA. I was never arrested how do you get state probation with no arrest.