I'd say more refugees than immigration per se, but yeah, it's about that too. The great thing about a metaphor about "othering" people is it can apply to a lot of things. Racism, immigration, jingoism, homophobia, etc.

It's taken mostly as a metaphor for apartheid because of the, you know, country and the apartheid they did in recent history and the apartheid done in the movie, but there's plenty of meaning to be found in "don't be a bigot and don't let people starve out of neglect and spite."