What makes you (or those in the article) an expatriate rather than an immigrant?
So, if you haven't decided that you'll stay permanently in the new country, but maybe instead you'll move to a 2nd new country, a 3rd and so on, then you might consider yourself an expat, but not an immigrant. At least that's how foreign students here, seem to refer to themselves: They're here for a few years, and then will probably leave, and they call themselves "expats".
And also, what about this: If you still have your identity in your home country (e.g. the culture there?), you'd think of yourself as someone from that country: "I expatriated from Home-Country". But if your identity is in the new country, then you'd think of yourself primarily as an immigrant to country New-Country?
I know that expatriate can colloquially mean a person temporarily abroad, but in this context, it refers to immigrants to Spain who generally intended to stay permanently.
I'm Irish, but once was an immigrant/expat in the US (in that I intended to stay permanently and to become a citizen, but things ended up not working out that way). I always thought of myself as an immigrant, but there were a lot of people I met who called themselves expats and never immigrants. Some almost seemed offended by the word. I think your comment about exceptionalism probably captured the reason why.