You misread the paper. The surnames Anderson and Thompson have white connotations, while Jefferson and Washington have black connotations. The researchers backed up their choices with data. From page 3:
> For example, based on data from the United States Census, 90 and 75 percent of individuals with Washington and Jefferson surnames are African American, respectively. Similarly, 90 percent of individuals with a surname of either Hernandez or Garcia are Hispanic, and 70 percent of Andersons and Thompsons are white.
> For example, based on data from the United States Census, 90 and 75 percent of individuals with Washington and Jefferson surnames are African American, respectively. Similarly, 90 percent of individuals with a surname of either Hernandez or Garcia are Hispanic, and 70 percent of Andersons and Thompsons are white.