Why do they mention only the country with the _second_ lowest obesity rate?
Probably because some insignificant (read: small) country has the lowest rate. It's easier to make comparisons when the population size is in the same order of magnitude.
http://articles.orlandosentinel.com/2005-08-28/news/SMOKING_...
Some researchers have hypothesized that America's obesity rate is somewhat correlated with dropping smoking rates.