Well,the author errs by making a blanket statement not all "Protestants" (whatever that term defines) are like that, however, some are -- and I know a couple personally who did that (now they are back to The Church)
you are correct that there are many non-Catholics who don't know anything about the Church, but among those are many who have perceived (wrong) ideas.
Among the Baptists I’ve met, I’ve never encountered anyone who gave significant thought to Catholic theology, unless they had a Catholic neighbor or coworker. In 40 years of listening to sermons, I don’t think I’ve ever heard the Catholic Church mentioned. It may have been at some point somewhere, but it certainly was NEVER the subject of a sermon. I’ve never heard it mentioned in doctrinal discussions.
In terms of what to believe, the discussion always centers on “What does the Bible say?”, not, “What do Catholics think?”
The idea that we define ourselves as ‘the opposite of Catholicism’ is ludicrous.