Its fine. Roots will grow in 2 ocassions. ONE- from anywhere on the stem that doesn't get bright light. Any part that is buried under the gravel obviously, but also from any node that might have been shaded by a nice dense patch of itself. The roots may have already been there when it was shipped to you, so don't worry. TWO, if the stem is allowed to reach the surface it will grow horizontally across the top. IME the horizontal growth Always puts leaves up, roots down.
If it bugs you, just pinch them off. The plant doesn't need them to take nutrients out of the water, it does that right through the surface of its leaves.
