Thanks for sharing the data, but your own data doesn't appear to support that comment.
If I'm reading correctly, the overall drop in US scores was 18 points. The drop in US scores of the two largest populations were 16 points and 17 points respectively. This isn't Sampson's paradox at all. This is exactly what it looks like, each subpopulatuon dropped significantly in score between the pre-covid test and this one.
To call a difference in score of 17 vs 18 (the overall average) an "exaggeration due to reweighting" is quite a misleading stretch of interpretation.