Written as the gospel song "Come by Here" ca. 1930 by Marvin V. Frey, who is not Gullah. Possibly taken to southern Africa by missionaries, but no proof of this. How it acquired the translated name 'Kumbaya' is uncertain. Either from the missionaries or possibly Pete Seeger during a trip he made to South Africa.
'Kumbaya" is possibly a word in one of the Angolan indigenous languages but there are similar words in Afrikaans: kom=come; by or na =near or beside. Where or how the migrated song was picked up in southern Africa remains uncertain.

No evidence of the song before Frey's text.