Cort, you and I come from about the same place and about the same time, and I also remember singing Pretoria, and a few other songs that were not of that time and place, like I've Got Sixpence. I don't know exactly why those songs found their way into the New York City area grade school repertoire, but I wouldn't be surprised to learn that Pete Seeger had something to do with it. He recorded nearly every folk song known to mankind, and those records got around to people who liked to sing the songs to kids.

I'd have a look to see whether Seeger and/or the Weavers ever recrded Pretoria, or see if maybe Burl Ives did, and that may explain how it came to you and me.