After Emancipation the freed slaves were also able to take a new name if they wished. Generally that of a famous person. Just a little more FYI. ;)
In one of the WPA oral histories of ex-slaves, a man who had not had a surname as a slave explained how he chose his. He had always heard the white folks talking about Jeff Davis, so he figured Davis was a good name and picked that.
Some of the freedmen kept their existing surnames (not always that of their most recent owner) but many chose a different surname.