Someone from Zimbabwe who moves to the USA for university, stays 10 years, then goes home to start a family or set up a business or whatever is an expat. There's a
lot of expats (e.g. from China or India) living in the San Francisco area.
An American who moves to Zimbabwe and plans to come back after a few years is an expat. If they change their mind, decide to stay and settle down indefinitely, they become an immigrant.
The article is aimed at people who are moving abroad for work, for a change of pace, for family reasons, and so on. Concerns about employment opportunities and housing (etc) apply to anyone who's going abroad for longer than a few weeks. Most people can't live off savings indefinitely.