Probably a fairly common cross over there for bushpigs, although not necessarily with formal lines, just farmers doing the odd cross here and there. My cousin has a bullmastiff x ridgeback, and frankly I'm of the opinion the boerboel is just a bullmastiff that's been in south africa for a while. South african farmers I know agree, and even prefer to call boerboels bullmastiffs. Here's my cousins dog- That's a big boar tusk scar in his armpit in the second from the bottom pic, has heeled up a fair bit in the pic above but is still faintly visible.