How do you condition someone to be loyal/obedient and not a liability? You haze them with the implication that a whole lot worse could happen, and then you test them. “You gotta promise not to tell anyone this, I’m trusting you” usually loosely translates to “I just told you something bogus and everyone is listening to see if you’re gonna spill the beans, and if so we’ll beat the everliving shit out of you until you learn”
It got the ‘trendy buzzword treatment’. There was a time when people were using it pretty heavily to describe professionals with specific skillsets and expertise sent to foreign (usually emerging) markets where hiring locals might be spotty. There was a time when, if an expat asked a local where expats hung out, the locals would interpret it as them asking where the foreign professionals would hang out, and usually they’d all talk shop/share experiences, that kind of thing.
There are of course multiple definitions but the corporate world started flinging it around like such. If you were chosen to be an expat you were basically ‘A team’ material - smart, reliable, trusted with a generous amount of autonomy, that kind of thing.
But it conveyed some sort of prestige, like ‘entrepreneur’. Now lots of people use it loosely as a colloquialism to describe anyone from a dyed-in-the-wool immigrant to someone who took a 6 month sabbatical to have an extended vacation on a sunny beach