From the Lemmy.world description:

"A generic Lemmy server for everyone to use. The World’s Internet Frontpage Lemmy.world is a general-purpose Lemmy instance of various topics, for the entire world to use."

And the logo is an earth. It does not forbid any community restricted to one specific country (neither should it, it's perfectly normal), but it sure isn't specifically tied to the US. I think a fair comparison would be if c/politics was China content only, that would looks weird too (even more so because of the language but well, surely you get my point).