The incarcerated number means nothing because of course there will be fewer people incarcerated when all drugs are "legal" (They're technically still illegal, but are now an administrative, rather than criminal, offense.)
I think the point that often goes unsaid with statistics like this is that decriminalizing drugs isn't the main policy. It was a complete changeup where they put lots of money into public education about drugs, establishing treatment facilities, providing easy access to MAT, as well as creating commissions to persuade addicts to go into treatment and restructuring the entire drug control/treatment enforcement agencies.