I'm guessing they might mean the literal roundness of the country, i.e. how close the geographic borders are to a circle.

Quick search suggests they might mean Poland.

It apparently does mean something (TIL):

https://gciruelos.com/what-is-the-roundest-country.html

But not sure this is what GP was referring to

Presumably an obese one.

https://worldpopulationreview.com/country-rankings/most-obes...