Migrants then because Trump told you it's the last time you have to vote.

Now that you cite the BBC, there are quite sizable communities of UK citizens living in Spain after retirement (ie permanently, without a short or medium-term intention of going back) and they consistently refer to themselves as "expats".

There still is a double standard though.

People from the wealthier first-world nations enjoy more international privileges — visa-on-arrival, stress-free travel, higher rates in currency exchange, dual citizenships, better societal structures and support for assimilation into foreign cultures.

Immigrants are either fleeing persecution or leaving their countries seeking a better life, requirements for visas and security checks, usually with not enough money, little privilege, and defacto distrust from foreign societal structures.

Relatively speaking, the typical expat can move around the world as they wish. Immigrants can't. So yes, immigrants, when they move, often do so, seeking to live elsewhere permanently.

It's never used that way in practice. No one calls Mexican seasonal agriculture workers in the US and Canada expats. No one calls Filipino maids and nannies in Singapore expats. No one calls Indian construction workers in Saudi Arabia expats. Regardless of the dictionary definition, expat is only used to refer to people coming from rich countries (US/UK/Singapore/etc.). Terms such as "migrant worker" are used for people coming from poor countries.