It's a good question but I would not agree at all that only black fighters can be classified as 'slick', that's ridiculous. Also, there are different types of slick fighters. Some fighters can be slick because they blend good defense and good counterpunching to be slick, others are slick moving forward, others are slick punchers, it can be applied to many things.

Slick, crafty, saavy, smart; all of those words are interchangeable to a certain extent. I believe what you are looking for here is the exact meaning of the word, right?