For those who are new to genetic genealogy, I should point out that there is no magic, instant roots DNA test. In fact, there are a handful of different kinds of tests. The one being used on Lopez Tonight is autosomal. Most genealogical DNA tests can only shed light on a single branch of your family tree, but autosomal ones offer a broader picture, providing some sense of your overall heritage. Typically, such tests break your heritage into continental chunks, telling you roughly what percentage African, Asian, European and (sometimes) Native American you are.
For a variety of reasons, results of autosomal tests should be taken as an indication, not an absolute. First, percentages being presented are those calculated to be the most likely; they are not definitive! Remember confidence ranges from your high school or college stats classes? Plus or minus X percent? These come into play. Three percent Asian, for instance, might just be statistical noise. Similarly, eight percent African might really be eight percent African, but it could also be, say, 11 percent or two percent when the whole range of possibility is taken into account.