When I was a kid, I decided that the best definition of Protestant was a Christian who was not Catholic or Orthodox.
While that may seem simplistic, I still sort of see it that way. The writer is correct in the meaning of the word “Protestant”. It is a negative term and has no meaning other than as a protest against the RC Church.
For that reason plus the lack of any central organization, once the Reformation occurred, it “went wild”, in that it spawned new churches/faith groups with ministers who went out on their own if they found even one piece of the Biblical interpretation that was in conflict with that of the minister. That is why there are thousands of denominations now.
I suggest that you read this article:
So many seem to think that the essence of being Protestant is to conscientiously object to what is or was Roman Catholic. A little history and a little linguistic research shows Protestant to be a much more positive word, referring to what the original Protestants stood for rather than what they stood against........Few churches ever adopted the name “Protestant.” The most commonly adopted designations were rather “evangelical” and “reformed.” ... [W]hen the word Protestant came into currency in England (in Elizabethan times), its accepted significance was not “objection” but “avowal” or “witness” or “confession” (as the Latin protestari meant also “to profess”).
-- from the thread History Lesson: Positively Protestant