When people say country, they mean the whole decentralised group of people, and the physical area, and a bunch of other stuff.
When they say nation state, the mean a government.
When they say nation state, the mean a government.
That's not what 'nation state' means at all - a nation state is an international state that is also a nation. So pretty much orthogonal as to whether they're a competent cyber force or not.
But this isn’t unique to nation states.
I favor APTs as a term, since it denotes any actor with lots of technical means and a political/strategic rather than financial agenda. Many APTs belong to nation states, but that's not always true!