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.

I’m a millennial living in US (although non native English speaker) and had no idea.

There are many things it seems GenZ is unaware of but it is very much a common, well-known expression for more serious people.

Does more serious equal older? I’m already too serious!

I know quite a few teenagers who are far more serious than my middle-aged self.

i've never heard of it.