Actually it is true! Some countries play much worse than others & you can even generalize certain playing styles with certain countries. Obviously not 'all' players from that country but enough that it is possible to generalize.
Is there really a country with the worst players? I don't know if I can say that. To my opinion each country has its specific habits, and sometimes you can see a bit of that in the way poker is being played. But calling that good or bad? That is a tough one.