What data are they using? If it's amount of coffee sold vs. population, at least Luxembourg is wrong. I know people who drive 2-3 times a year around 300km from Germany just to shop gasoline and coffee in Luxembourg. Both are so cheap that it's still worth it. Cause there is no tax on coffee it's 20-50% cheaper as in Germany. The same for Belgium. So germans and belgians love to buy coffee in Luxembourg.
Edit: exactly this question is written by the author of the linked article. So it is plausible that the data or the result from the data is wrong.