This infographic is intentionally misleading. The author is adjusting the radius of the circle based on the export numbers, not the area.

For example, according to the rendered source code, America for 2018 has a radius of 75.05, Germany has a radius of 9.12, for a ratio of 8.22. From the data[0], America has a value of 10508, Germany has a value of 1277, for a ratio of 8.22.

However, since this is the radius, the area of America's big red dot is 17671, while the area of Germany's is 261, for a ratio of 67.7, or sqrt(8.22).

0 http://armstrade.sipri.org/armstrade/html/export_toplist.php