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.