From the Guardian after a minute's Googling: "New Zealand has one of the highest incarceration rates in the developed world, with Māori people accounting for more than 50% of all prisoners, despite representing only 15% of the overall population. Some 90% of prisoners have a life-long diagnosis of mental illness or addiction." (https://www.theguardian.com/world/2018/jul/29/yoga-herbs-and...)
Seems like there's an argument to be had, which makes me view the rest of the piece suspiciously.
[Edited to insert context on what "this claim" is]