This inaccuracy is a common problem with graphs and charts. The proprotions do not match in this case. Maybe the ring has been designed by a designer, constructed with old data, and now it is easy to change the numbers in the graphic, but difficult to adjust the size of the ring segments? Or maybe somebody has just forgotten to update the ring segments when the last update of the numbers was made.
Sometimes fancy, but graphically inccurate, charts are used to cheat and deceive, by representing small things larger or big things smaller. Putting a pie chart in 3D can have the effect of altering the perceived information, because if you're looking at the pie chart from above but slighly sideways, the part of the chart closer to you may appear larger, and since you can rotate the chart before rendering the final picture the choice of that part is yours.
Sometimes fancy, but graphically inccurate, charts are used to cheat and deceive, by representing small things larger or big things smaller. Putting a pie chart in 3D can have the effect of altering the perceived information, because if you're looking at the pie chart from above but slighly sideways, the part of the chart closer to you may appear larger, and since you can rotate the chart before rendering the final picture the choice of that part is yours.