Having lost the last duel, Le Gris automatically becomes guilty, and there is no point in additionally mocking the body, putting it on public display. There is clearly a reference to the original source here - according to the chronicles, Le Gris did not die, although he lost the duel. So he was hanged like a common criminal. The director just played this moment in a different way. The body is mocked to disgrace the person and his name.