Thank you for your very good reply. You have clarified a RCC definition, and you are most likely correct that given the European context, those people are surely renouncing Christianity in its entirety.
My own father repudiated any association with the RCC in 1974, having undergone a water ceremony (we utterly deny that such is Christian baptism) when an infant. He was born again in 1974 by faith in Jesus Christ as his personal Savior.
He didn't bother with filing anything, but took much delight in witnessing to Catholic priests when they came to visit, and wrote many letters of testimony of his genuine conversion to Christ in 1974 to the area Catholic priests.
We don't care, really, what the Vatican would say about who should be using what definition, however. We don't allow Roman Catholicism to determine either history or etymology.
Further, it is interesting that the article begins with illustration from some old Camp Meeting songs originating in Appalachian camp meetings a hundred or more years ago. These are songs I am sure would never be heard sung in a Roman Catholic church. These are great songs of Bible-believing (yes, sola scriptura) Christians.
I wish you were right.
Unfortunately, many modern Catholic hymnals have way, way, way too many modern Protestant (yes, sola scriptura) hymns in them.
Really a pity, since we have 1,950 years of a musical patrimony to draw upon. But traddies like myself are trying to bring back the old classics.