The name "Christian" includes Catholics
We Catholics are Christians, are we not? So the term "Christians" cannot mean solely "Protestants." It is as simple as that.
This is not trivial. Why not? Mainly because quite a few Protestants love to claim we Catholics are not Christian. We have all had Protestants challenge us by saying, "I know you are Catholic -- but are you Christian?" And remember the TV preacher who insisted that he had no way of knowing whether Mother Teresa of Calcutta was a Christian?
It is even a life and death matter. Did you see the Catholicnews, Zenit and other recent news reports about Michael McIlveen, 15, of Ballymena, County Antrim, whom Loyalist/Protestant bigots recently beat fatally with baseball bats simply because he was a random Catholic? A friend of mine reports that before the funeral, a Protestant announced that young Michael could not go to Heaven unless he "repented" and "was saved," because as a Roman Catholic he was not a Christian. Fortunately, Michael's young Protestant friends attended his funeral.
All this is why we should definitely remember in our conversations that the name "Christians" includes us Catholics (and the Orthodox and others, too, of course) as well as Protestants.