Red plum

I found these in a yard of a house I visited. I'd never seen ones like these before. I put them in a pot of dirt and am hoping they'll sprout!
I think I found them! I was looking for the scientific name for this post. I assumed it was a relative of what I've grown up calling Hog plum. I did a search on this cool site I came across recently and found exactly this fruit!
I hope I'm right! It looks like it's from Easten South Africa and said to be tasty.

Harpephyllum caffrum
http://tropical.theferns.info/viewtropical.php?id=Harpephyllum+caffrum