Nashville had already decriminalized weed as of 2016. I only find one other case (Houston) where it was a prosecutor making a policy decision not to prosecute weed, ahead of the rest of the government. Honestly, just read the rest of the article you cited -- it matters that a lot of the rest of the city government was on board for it, but it still left a little bit of a confusing way to go about it even after decriminalization, which the chief of police among some other people pointed out, along with the idea that yes weed should be legal so maybe it's a good thing.
Left unsaid in among all of that is that selective enforcement by police and prosecutors in almost every case works out, in practice even up to the modern day, to be racist selective enforcement. Honestly it's better for the legislature just to make it legal. I'm not trying to throw cold water on any prosecutor who wants to take the initiative to do a good thing if they can make sure it'll work out right, but generally, the prosecutorial portion of the government isn't where you want to be making your creative departures from the law the way the legislators wrote it down.