All of that ethnography is interesting and accurate. "To call a spade a spade" in modern colloquial usage means "let's not equivocate. If a man is broke, say so, don't describe him as 'temporarily overextended."
In the U. S., a derogatory term for a black man is"a spade," derived from the fact that in a deck of cards, the suit called spades is black.
Therefore, to use the phrase in the way that the OP did is an sad attempt to make a racist joke, regardless of what the ancient Greeks meant. Let's not equivocate...