The best we can say for that chart is that there is some relation (not necessarily casual) between GDP and mathematical education levels.
The causal factor could be anything - but it’s a damn pretty curve. It at least suggests that measuring a country’s gdp can give you a ballpark figure for it’s mathematical education levels.
Might be a novel premise for funding to explore if math is a causal factor.
There’s probably a better number than GPD/pop, considering the big outliers have exceptional inequality or equality in vietnam’s case.
There’s probably a much better line between median (or even better yet, first quartile) education funding and math scores, and a similar correlation to OP between GDP and education funding.