Even though I've only come across the term occasionally, I think it really just means eastern NC-style whole-hog barbecue where vinegar-based sauce is used. I friend brought back some pints of Bullock's from Durham a while back, and it was clear the vinegar sauce had already been added to the product before packaging. The vinegary flavor was noticeable, and bits of red-pepper flakes were mixed throughout the meat. Oddly (to me anyway), this vendor cooks in gas-fired cookers-- no evidence of smoke on the meat whatsoever, but I've read it is one of the more popular in the region.