Tolkien never said publicly the work was Catholic or Christian and did not wish that association to be made. You did that by digging into his private letters, and found a note to a priest.

When asked by a fan about his work, Tolkien referred to religious ideas in the most abstract way:

"But since I have deliberately written a tale, which is built on or out of certain 'religious' ideas, but is not an allegory of them (or anything else), and does not mention them overtly, still less preach them, I will not now depart from that mode…"

Then you came along and slapped "Christianity" all over it. He writes in the 1966 preface of the origin of the story:

"I had little hope that other people would be interested in this work, especially since it was primarily linguistic in inspiration and was begun in order to provide the necessary background of 'history' for Elvish tongues."

No talk of Christianity at all. Unless a biography had been written of him after he died, no one would even know he was personally Catholic.