Expat supposedly not staying and not called the place home.

Immigrant is really moving in.

You add the economic adj the response is by another - expat has money ei no

I think it is also about how rich you are? (Coming from an expat/economic immigrant)

I think it also hinges on the degree to which someone cuts ties with one's country of origin. "Expat" implies continued ties to a homeland, whereas "immigrant" implies an intent to turn the new place of residence into one's new home. There are obviously exceptions and blurred lines there, but that seems to be what I've observed.

Expat says nothing about why a person is living somewhere other than their homeland.

Legal status in the country also probably, economic migrant is a euphemism

euphemism for what?

It's a word that immigrants use so they can continue to hate immigrants.

Or at the very least distinguish themselves from the immigrants everyone else hates.