The above linked data show self-reported cannabis use within +/- 10% over the relevant pre-legalization period (before 2012), if anything with a slight advantage to whites. Drug arrest and incarceration rates vary by much, much more (factors of 2-6 between whites and blacks). Against that, use rates of 15 vs 13ish vs 12.5ish are as good as uniform , esp. on a survey with all the inherent variability therein (even for one as competent and longstanding as the cited work).
So what's the quibble? That the shares aren't exactly equal? Or that there are other demographic cuts with larger differences (and, y'know, aligned carceral disparities)? Or that cannabis use isn't representative of 'petty crime'?