It's not about slavery. It's a Christian gospel song;
"Swing Low, Sweet Chariot" was composed by Wallis Willis, a Choctaw freedman in the old Indian Territory, sometime before 1862. He was inspired by the Red River which reminded him of the Jordan River and of the Prophet Elijah being taken to heaven by a chariot"
Just because it was written by a freed slave doesn't mean it's about slavery so stop imagining things that aren't there.