I'm sure having a nation-state is a major factor, but I bet it also has to do with the average wealth, geographic location, historical alliances. However, I'd put my money on skin color as the biggest factor.
As an example in favor of your conclusion, I propose Greenlandic. Geographically really close to Iceland, is the sole official language of an autonomous country, significant cultural heritage (with even a famous [possible] dwarf planet named after one of their historic gods). However—unlike Iceland—Greenland is not a wealthy country, and tend to have darker skin color then Icelanders.
You are being overly pedantic. Country is not a strictly defined term. Sometimes it is used as you imply here as sovereign states which Greenland is not, but often it is used for other political entities as well. E.g. you often hear people speak of Puerto Rico as a country, and you also hear people from the UK pride them self that they are a country of countries (the former singular “country” meaning sovereign states, and the latter plural “countries” something else).
If the UK is a country of countries then Greenland is most certainly an autonomous country. The Wikipedia article for Greenland has the word “country” mentioned 14 times, so I’m certainly not the only using the term this way.
