He didn't admit that he was smoking and driving. He smoked and then drove. From the sound of it, it had been around an hour till he drove after smoking. Highs last entirely different lengths.
But sounds like he was pretty "sober" by the time he got home.
Being that weed is decriminalized there, he probably would have been fined. There is a good chance that they were looking for a better punishment than just a fine and curfew seemed like a better way to do that.
My friends drive high all the time and I have never felt that I was in any sort of jeopardy (I don't smoke). I do think it is sad that it's still illegal in most places. I think driving tired or on an energy drink high is more dangerous than on a weed high.