> The study was carried out amongst a demographically representative sample of the online population aged 16-64 in the following territories: Argentina, Australia, Brazil, Canada, France, Germany, Italy, Japan, Mexico, Netherlands, New Zealand, Poland, Russia, South Africa, South Korea, Spain, Sweden, United Kingdom and United States. The study was also conducted in China and India but results from these two countries are not included in “global” figures due to the size and nature of these markets. In total, 43,000 internet users were surveyed with higher numbers of respondents in larger markets.

They literally just surveyed first world users and made no effort to control for class or other confounding factors that influence musical taste. This pretty much only tells us what first-world city-dwellers like, not the world generally. We're no closer to knowing whether country music is truly the most commercially successful music genre worldwide, but neither are we any closer to disproving it.