I couldn't find the UN report that they got their chart from. However, they only said "providing adequate calories and nutrients", which is a low bar.

I'm guessing 1.5kg of dry white rice can be found for around $1, and that covers the "calorie" needs. The rest of the budget can be spent on vegetables, nuts, beans, lentils, etc. to cover the "nutrients". It would be a pretty sad diet, but I think you could hit the numbers they're looking for.