It doesn't surprise me, rock wool is rather an efficient material.
Its big interest is the price, and this is why many acoustic panels are made with rock and/or glass wool. Moreover, it is a material that is very easy to find.
Then it has some drawbacks:
1. It is very polluting to manufacture --> many human associations have been created to prevent the establishment of a factory near their homes.
2. Little is known about its effects on health (what is certain is that this material emits micro-particles and the manufacturers of these materials advise that great care be taken when handling this material).
3. It is not the insulation that will be the most durable over time in terms of performance.
In summary, it has its qualities and its defects