The terminology is chosen selectively to deliver a provocative headline. At most US universities, the title "professor" is the highest academic rank (there are chaired professors, but that is just a full professor with the benefits of a chair). "I taught classes at four universities" doesn't draw the same number of clicks.
In the US, there's the internal title system [1] that varies from university to university. Sometimes adjunct is synonymous with lecturer, sometimes lecturer is above adjunct.
Few undergrads really pick up on the internal ranking, and just call their instructors professors. Anyone outside of academia is just going to call somebody who teaches at college professor, even if they're not a Professor. it's kind of like talking to a paleontologist about dinosaurs, or complaining to an astronomer that pluto should be a planet. You know, it's internal technical jargon.
Anyone writing such an article surely knows the difference (or at least should know the difference). It's even worse if the title was written to take advantage of the fact that the average reader thinks everyone teaching college classes is a "professor" with all that the term implies.
I was only responding to the question of how someone could be a professor at four universities. The questioner is correct and the title is not accurate.
The author didn't bury the lede, "I was an adjunct, and I could only tolerate the stress and exhaustion for two years." is in the first paragraph.
What to call a college instructor is a hard problem for the instructors own students! [1] You aren't taking issue with the layperson view of "everyone is a professor", furthermore that's the approach advised in [1]
You're asserting it's a clickbait title. I disagree.
I agree. It is somewhat misleading to represent yourself as a "Professor" when you are an adjunct, non-tenure track instructor/faculty member.
In response to the earlier question which you also answered:
In general, in American Universities it goes Assistant Professor --> Associate Professor --> Professor at ~5-10 years between each step (the exact details vary depending upon discipline and University). In science, these are usually the people who are writing grants and are at the heads of labs. Usually you must be tenure-track to advise graduate students.
Then there may be another class of 'lecturers' who are not-tenure track but are still considered faculty-members. There is not always a distinction here between lecturers and adjunct instructors, however. Lecturers' main role is usually instruction of undergraduate or graduate students.
Finally, there are the adjunct instructors, whose primary role is the education of undergraduates and who are paid much smaller amounts of money for their work relative to tenure-track faculty. This is a relatively newer class of University employee, and it is definitely a very difficult career. I imagine most adjuncts either have other careers or are attempting to break into the tenure-track rank, although I do no know how often this happens.
In addition, in science there might be 'Research Scientists,' 'Research professors," or 'Staff Scientists' who work under a tenure-track faculty member. They are often somewhat equivalent to lecturers, except they do not instruct undergraduates but instead are usually full devoted to research. It's essentially a "Super-Post Doc," but hopefully with a salary one can reasonably live on modestly.
And for completeness: In science, people do Post-Docs following the completion of their PhD. They are non-faculty jobs under a tenure-track professor where one conducts full-time research, usually for 2-3 years, although some people must complete multiple Post-Docs. The usually idea is to find a faculty job after your post-doc, but I think a majority of people end up filling some ancillary position in science or leaving science entirely, because there are unfortunately many more post-docs than there are faculty positions.
It gets even more complicated when you add in MDs and hospitals to this academic situation.
