the clothes styling is typical for the time "sinterklaas" lived in,.check old paintings from like Rembrandt and other european painters from that period.
everybody dressed up like that in lower and middle class, so no race difference.

not shure about the "negro parodies" but what i understand. the use all the difference so nobody feels affected,.hence that most african-dutch dont have a problem with it,. for them swarte piet is a moor blacked by coil dust,. and for the moor-dutch its a afro in a mideveal costume..