I find it hard to take sweeping statements like this seriously. What makes Scandinavian countries any more or less earnest than, say, Germany or France? This seems no better than to say, “The French make great lovers,” or “The British are terrible cooks.” Absent any evidence to back them up, many such statements in PG’s essays seem to be an expression of his prejudices. The very least he could do is to provide some criterion the reader can use to test “earnestness” at the population scale.
In this case, I imagine that he started from “Scandinavia is the region with the highest number of startups per capita” and inferred that this must mean that they are more earnest, rather than going the other way around.
They are hard to take seriously because they are not earnest, it's cherry picking to prove a point, based on false premises.
Scandinavia is not even a country, it's like saying "Benelux has the higher GDP per capita of Europe" but Luxembourg has more than two times the GDP per capita of Belgium, the three don't even speak the same language and 20% of the Luxembourgers have Portuguese nationality.
I imagine that Scandinavia has a good reputation as role model society among his audience so he chose Scandinavia.
I had a Swedish girlfriend, still have many friends there and my wife is half Danish, so I agree with the sentiment, but the facts are definitely not there.
If the parameter is "startups per capita" and the geographical region doesn't have to be a sovereign country (Scandinavia is not) then I would say that in Europe (the continent) London and Berlin have the most startups per capita (London also in absolute numbers), despite being two very different places with a very different idea of what being earnest means.
I mean, sure, not completely, they definitely had some of their population deported by Nazis, but it wasn't such a major impact as elsewhere in Europe.
The WWII in Scandinavia was particularly bad, including the occupation of Norway and Denmark.
https://en.m.wikipedia.org/wiki/Operation_Weserübung
They did escape the contemporary ones the same way any other country in Europe did anyway.