Actually, if the arms are solid enough to push the air, and the rock is floating without any friction between it and the ground, then it should be able to move, given the surface area of those arms. It might not be able to go very fast, but it can still go. If the rock were smaller, that would cut down on air resistance, allowing it to accelerate faster, but the large rock is good for storing momentum, making it harder to stop. The arms would be able to propel it even better if they were scoop-shaped, but given that there's no visible detail, it's impossible to tell if they are or not.
TL;DR: I don't think the arms are a problem.
TL;DR: I don't think the arms are a problem.