I'm afraid I can't account for an individual's misapprehension. Words mean what they mean. Sioux is a fairly helpful example, in that one could indeed be part of the Sioux nation and be ethnically Santee, Yankton, or Teton. And one could also obviously be adopted and be part of the nation.
Words change their meaning all the time and mean different things to different people and at different times. That's language for you. And if you're seeking to define ethnicity on, eg, DNA grounds you'll soon realise that's futile too
Ethnicity isn't defined by DNA. That would be a misunderstanding of the concept of ethnicity.
I didn't say it was necessarily. My assertion is it can't be any better defined than the concept of nation in any consistent way that doesn't create other issues or controversies that too often aren't especially helpful. It's even worse when it's further muddled with reigion
I'm not sure why you brought it up then? Regarding the distinction between nationality and ethnicity, I think the example of the Sioux that you referenced above is quite a helpful illustration.
Helpful to what? Logic chopping spurious distinctions between so-called ethnicity and nationhood? Let me try this. Are Saami a nation or an ethnicity?
Helpful in illustrating the distinction between the concept of ethnicity and the concept of nationality. Before we move on to the Saami, it would probably be useful to close out the example of the Sioux?
So you contend the Sioux are a nation made up of ethnicities. Whereas Germans, say, are an ethnicity made up of >1 nation: Germany, Austria, maybe some of Switzerland (though Swiss feel they're 1 multilingual nation). While Kurds, Basques, Catalans, Scots are what? Unless nation doesn't count...
Ethnic groups quite commonly cross over national borders. In the same way nations typically contain multiple ethnic groups.
What are the national borders of the Kurds? Or are they denied the status of nation because they don't have a state? Do the Scots only become a nation if they get independence? It's nonsensical. As I said, you're entitled to differ but there's no meaningful consistency. I know because I've lived it
The Kurdish people are quite a good example of an ethnic group that is spread across multiple national borders.
...without a state. Which is why the Palestinians are so f*cked. Most of what was Palestine having been seized, are Israelis now the nation there, or just a subgroup of an ethnoreligious tribe mostly from Europe? It's all a bit of a mess sadly and too often just leads to conflict
The modern State of Palestine has existed since 1988.
Palestine is way older. As a state it's still not fully recognised eg by US or UK