A rock garden is not merely a bunch of rocks tossed around on the ground. It is, literally, a pile of rocks, carefully arranged in an attractive way that creates small, confined pockets. The pockets are filled with the lean, sandy, gritty soil mixture that is required for the cultivation of alpine plants.
A rock garden, with its lean soil and confined spaces designed for small plants with tiny root systems, is not a place one would or could grow much in the way of vegetables. Rather, it is a highly specialized artificial environment created in order to grow alpine plants, which are normally found in rocky terrain in the mountains.
A raised bed out can be built out of just about anything. Any of a wide variety of materials, including rocks, can be spread over the surface of the soil to serve as a mulch. But simply choosing to place a bunch of bricks on the surface of the soil in a vegetable garden, be it a raised or traditional bed, does not mean that one has created a rock garden.
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams