I'll answer your reply first and I'll see whether I can respond to the other poster later today!
I'd say it differs, to be honest. China is a country with a corrupt government, huge inequality, and a gdp not up to developed standards. So you'd definitely be able to make a case for social conformity as important to high social trust. But Scandinavia, the Netherlands and Canada are just not conformist societies so it doesn't seem to be necessary, if perhaps useful.
I would add that social conformity does not trust make. Conformity might just be perceived as a 'mask' where people act how they should in public, but are still deemed selfish and untrustworthy behind their behavior. I can imagine that conformity might work for and against impersonal trust.
In the study, it's a society where more than fifty percent of the societal inhabitants indicated that 'most people can be trusted in contrast to that you can't be too careful in dealing with people'. So, basically, people aren't out to get you and you can trust them.
Omdat wij gewoon superieur zijn ;p. I dunno, according to the perceived corruption index Belgium is perceived as somewhat more corrupt than the Netherlands by its inhabitants. Our GDP per capita is about four billion dollars higher than yours. Belgium is also fractured between a french and dutch speaking population that might impair societal trust.
Well, according to this study, people get more nervous on a train as its ethnic diversity increases. journals.sagepub.com/doi/10.1177/0146167213499377
Remember that the study mentioned mentions impersonal trust (trusting the whole society instead of just your neighbours of small village). Who are you inclined to trust more? The people that look like you and behave like you and which you identify with? Or relative strangers that you just can't figure out? Multiculturalism has not made the Dutch, for example, relate to Muslims as part of the in-group. We (unconsciously) perceive them as the out-group, higher educated people have just been socialized better to hide it (which you could call political correctness). nytimes.com/2011/01/11/science/11hormone.html?_r=1
When I go to Groningen or to Rotterdam, I meet people that are like me and identify with me; it just helps. And because we all have money, there just isn't much of a reason to screw each other over.
Consider Africa, which is very multi-ethnic and in which states are usually politicized along ethnic lines. Wider society doesn't care about you; it cares about the in-group. In this article, written by Francis Deng who, if I remember correctly, if from Sudan, ethnic diversity is viewed negatively.
'A few states in Africa enjoy a high degree of homogeneity or, at least, a relatively inconsequential diversity. Botswana, for example, reflects exemplary cohesiveness, democracy, stability, and sustained growth.'