Pretty sure it's about belt rank, so the one you see on your usercard, this:
Being belt rank 1 means you've got the highest qi in your belt, so if you've got 3999 qi, you most probably get belt rank 1, unless someone else also has this amount of qi, then the one that got it first probably has the highest rank.
And still, when you get belt rank 1, you're not ensured to get the achievement, as they are broken.
Also I have no idea why your belt rank is 0, probably bugged.