We normally use slick to describe something that is smooth or glossy. The rocks are wet and really slick. When we use it in a figurative way, we mean the action the person or people took was a smooth and/or efficient. He has really slick dance moves. In your example, I would think they mean that whatever the person did was a bit impressive. We usually use slick when we have the feeling of being slightly impressed with what someone has done. Hope this helps. :)