I'm not familiar with the South-African breeder you're referring to, so I can't comment on his line, but the link you've provided shows dogs with some (English) Staffordshire Bull Terrier influence, no doubt due to the European import blood since there are quite a few AmStaff lines over there, especially in eastern Europe that were established by crossing Pits and AmStaffs with English Staffies some 15 years ago. I'm in no way implying that your breeder's dogs are crosses, just that their appearance suggests a connection to the Hungarian, Polish and Russian stock which was initially a combination of aforementioned breeds, but has since been purified and is now a straight AmStaff population with a recognizable appearance which still differs a bit from the common American type. Nothing wrong with that, variety is the spice of life.