I looked it up too. Netherlands is 153rd in inequality compared to South Africa at number 1, using the World Bank income GINI. I don't know where the data in this article came from. The author is talking about wealth, and the WB data is income, and these two are very different measures. In the link you provide, there is a "wealth GINI" and that shows the Netherlands ranks at 46th worst, above the average. But a different measure of median-to-mean has Netherlands at 154th. The US ranks 9th worst in median-to-mean, 6th worst in this wealth GINI, highest of all developed countries.