Indeed, even in the limited and familiar example of English speaking culture, there are two completely different reasoning chains for the two synonyms used by English speakers to refer to our planet, "earth" and "the world." "World" derives from "wer," the old English word for man/human. Thus, the world is simply the place of men or humans. The word "world" was used for centuries to encompass the entirety of physical reality; water, land, sky and (once it was understood) outer space. But in the 1600s and 1700s, as it became popularly understood in English speaking cultures that humans live on a planet, the word "world" gradually became synonymous with this planet Earth. Other words became the preferred references to the entirety of physical reality, namely "universe" and "cosmos" (the latter deriving from the plural of the Greek word for "world").There's the land and there's the sky and the sea, and people talked about the land as the place they lived on, and so a word meaning "the land" ended up being extended to apply to the planet once the idea of it as a planet took hold. But there could be other reasoning chains. A culture's word for their entire world might translate as "Everywhere." Or "Under-sky." Or something else.
In fact, in the case of the English word "world," the exact opposite chain of verbal logic was applied. The species' name for their planet became "planet of our people." But these two opposing chains of logic would, of course, produce similarly similar names for a people and their planet.So it strikes me as the same kind of logic problem as assuming that a species' name for themselves would mean "people of our planet," like Vulcans from Vulcan or Sontarans from Sontara or whatever.
Sometimes. But it's worth noting that the exact opposite is sometimes true. Ancient people in the near East and Europe referred to the other side of the world as the Antipodes, a phrase that eventually came to encompass the unexplored Western Hemisphere for pre-Columbian Europeans. The prevailing wisdom was that if any intelligent life existed in the Antipodes, it was not human life as Europeans knew it. Why should it be, on the other side of the world, where everything worked differently. Except it was.The problem is that it's too basic. We always assume that everyone everywhere will think exactly like us, and then we actually go find out and discover that they actually went in a totally different direction that never occurred to us.