Why do people wave at me while theyre driving?

Yesterday some intimidating big bald headed tattooed racist looking white dude went out of his way to wave to me and said Hi! While he was driving on the opposite side of the street and today a pretty black girl stuck her hand out the window passenger side to wave at me and smiled. What does this mean? am I doing something wrong when I'm walking the streets? It was in broad day light so I wasn't in their way p.s. I'm black by the way. Help!