I would try to draw parallels from Russian language.
In Russian the word for country is strana.
It has different meanings:
- A sovereign state.
- An area with distinguishing features such as landscape, flora, fauna, people etc.
As you may know, Russia and the former USSR had some sub-national entities called "republics". But we do not call them "countries" because they are not independent. But if they become independent, we start to call them by the word for country. For instance, Ukraine was not a country when it was part of the USSR, but now we call it a country.
This reflects the first meaning.
The second meaning of the word one can observe when we can say that "Antarctica is the country of eternal ice", "Tibet is a country of the high mountains". In these sentences we do not mean that these are independent states but merely areas with distinguished features. We also could use the word for kingdom here, figuratively, without implying they were monarchies.
Thus Scotland may be viewed as an area with distinguished features, such as landscape, mountains, folklore etc.