As someone living in Norway who has been quite interested in the subject and read a lot about it. My understanding is that nordic countries tend to come at the top, not because people are jumping around with joy in the streets. More likely to find that in South America or Africa. Nordic happiness is a mild happiness. It is really about having few people very dissatisfied with life rather than having super happy people.

There is little of the social conflict, poverty, health problems etc which plague many other countries.

That is what these things measure. Latin American countries would typically get pulled down because there is a signifiant portion of people who don't have very nice lives. This is what I've heard from foreigners living in northern Europe. They notice that there are very few people you observe who look genuinely dissatisfied with their life.