While that does ring quite true to me (I'm an 'expat' immigrant myself, although moving both to and from rich countries), I think the piece hit a bit off target: It's a 'rich' thing, not a 'white' thing - the white polish plumber or builder in the UK is unequivocally considered an immigrant, the software engineer is more likely to be an expat.

Also, one deeper, to my ear, 'expat' has a flavour of intending to return, where immigration generally sounds more one-way and permanent - which of course again parallels the 'rich' narrative: it's much easier to intend to return to your rich country of origin than it is to return to a poor one.