From TFA:

"As Flynn and Shayer note, Scandinavian IQ declines might well presage future trends in other countries. It may be that, once we’ve made our schools as good as theirs, we’ll see our Flynn effect max out, and then whatever channels feed their anti-Flynn effect will show up in our data, too."

The summary of the study the article mentions and links to doesn't show if the trend is an average of some sort or if it's the result of a more self-selecting sample region.

Unfortunately between that and only having first-hand local culture knowledge, I am unqualified to speculate in a meaningful way about the differences in culture and environment.

Also, just because a trend is increasing does not also mean that there's an underlying masking effect or that there isn't overall convergence. Ideally at least similar studies would be performed on a global basis if a global comparison is occurring.