(Personal opinion only)
It seems too short to be a 'collage' (Unless we're discussing a collage of individual notes, or of 3 note phrases, which would describe nearly all music)
I can't identify anything that it would seem to be derived from.
If the Church Hymnary attributes it to Carter, that should stand, unless someone give convincing evidence to the contrary.

As I said, just my opinion.

Cheers
Nigel