It's an uncommon expression then. The commenter might be British. Anyway, anyone reading this thread knows it now.
I recently met someone who uses the expression "country mile" all the time. Hadn't heard it before but it's cool. "That's more popular by a country mile" Country miles are obviously better than city miles. So now I'll probably end up using it.
A country mile is often hot and dusty and walked uphill both ways by your grandpa. Time stands still and the cicadas buzz. It’s bigger than a city mile even in how much imagination it takes to conjure.