I think "anonymous" would be the term for lyrics or tune of unknown author. Depending on the definition of "traditional" it may or may not qualify.

First, it's not been documented to be transmitted by oral tradition and varied by folk process (though it is entering that tradition now, as some of us have learned it, sing it, vary it, and pass it on to others). Still, the fact that most of us who do sing it all learned it from a single source recording makes it rather different from oral transmission in the case where there is no reference-able single source version.

Also by some definitions it wouldn't be traditional because it can't be traced back long enough in history. I usually go by 100 years, and this one is documented only since the 70s and at best to the 1930s if we take Packie's account at face value. (Maybe Kathleen wrote it?).

But honestly, who cares how you define the term "traditional"? Personally I just state what I know (and don't know) about its origins, and leave it at that. It's a great song.