I think it’s false taken simply as it stands. There are plenty of Protestants who are learned in church history. However, I think it is impossible to think of history in a certain theological way and still be Protestant, and that is perhaps what Newman meant. Or at least, to have the deep desire to claim the entire Church’s history as one’s own leads to a certain tension with Protestantism, because however much one emphasizes the pre-Reformation roots of Protestantism there remains some kind of break with the past inherent in being Protestant.
This, of course, does not automatically mean that one becomes Catholic. There’s always Orthodoxy. And living in tension is part of the reality of this life. So I think Newman’s statement was false but contained some truth.
Edwin