Well, it's important to note the alternatives. First, lots of resource-rich economies develop the "Dutch Disease". In one interpretation--the interpretation that Krugman expounds--the resource sector comes to dictate a nation's monetary policy, which produces disadvantages for manufacturing and service exporters. In another interpretation, resource-rich economies focus first on extracting maximum wealth and only later focus on distribution or reinvestment. This is especially true for nations that have not developed a system for distribution and reinvestment by the time that they begin extracting their resources. By contrast, the Norwegian people developed a strong set of national institutions for distribution and reinvestment first.

Second, consider the historical alternative. The Norwegian economy is that it was a poor country for a long time. Their 2013 GDP is 98.5 times larger than their 1960 GDP. But even as a poor country, Norway participated in the so-called Nordic Model, which promotes many of the same standards as the Human Development Index (individual autonomy, economic mobility).

Combine the first phenomenon--an exceptional combination of monetary policy, distribution, and reinvestment--with the second--distribution and reinvestment directed parallel to the HDI goals--and I think this phenomenon is fairly easy to explain. This combination also explains the so-called Norwegian paradox, which highlights Norway's growth in spite of its low R&D investment.