The difference in expatriate and immigrant is in the power/influence/wealth of the host country compared to the native country.
A person that prefers to be associated with the host country is an immigrant, as it's considered an improvement in station to be associated as "from" there. An expatriate is an expat because they don't want to be associated as being "from" the host country, but their native country, ostensibly because it's a Western nation of higher power and wealth. This distinction is inevitably both classist and racist as the differences are related to both issues.
A person that prefers to be associated with the host country is an immigrant, as it's considered an improvement in station to be associated as "from" there. An expatriate is an expat because they don't want to be associated as being "from" the host country, but their native country, ostensibly because it's a Western nation of higher power and wealth. This distinction is inevitably both classist and racist as the differences are related to both issues.