A wrong turn is a traffic violation. Law enforcement's involvement came from a traffic violation, speeding. This started with something every driver has done; speed. Some may be able to say "I've never exceeded the speed limit by that much." None can say, they've not made the mistake of speeding.
Three mistakes here and the one I see the most attention paid to is the least of the three in "criminal penalty."
Before we jump to "weed > speeding," the fine for 21 mph over the limit is $227.50. The maximum fine for weed possession is $250, and with only a gram he's looking at their minimum, $100.
Again, the insurance is the story. That could be as much as a $500 fine and could end up costing him his drivers license for a year.