The designer went to substantial effort to make the area of each figure proportional to the number displayed (it says something about modern statistical computing that the my quickest way to check this was read the image file in R, use cluster analysis to find the figures, then tabulate).
However, it’s not remotely true that typical Malaysians weigh nearly four times as much as typical Cambodians. The number is the proportion above a certain BMI threshold, and that changes quite fast as mean weight increases. Using 1971 US figures for the variability of BMI, you’d get this sort of range of proportion overweight with a 23% range in mean weight between the highest and lowest countries.
Reference: Overweight Populations in Southeast Asia