I don't know if there's more in Chronicles, but it looks like this came from a
Tauren creation myth from Folk & Fairy Tales of Azeroth. If I'm understanding it right from a quick look, it sounds like An'she was wounded by the Old Gods or their minions, then he and Mu'sha took up their orbits to protect the land from more "shadows" (I assume preventing more Old Gods from coming?), with Mu'sha tending to An'she's wound. And apparently the Tauren believe that the light you can see just before dawn is An'she bleeding light.
The idea that this bleeding is slowly turning An'she towards the Void would be plausible under what we know of Light and Void entities, but it's still a big assumption- especially given that the sun is still clearly giving out light, so even if this is happening, she clearly hasn't turned
yet (and therefore shouldn't be An'shuul, which already seems to exist as a Void entity). Maybe Mu'sha's healing is keeping An'she from falling to the Void, and given An'shuul's name and the Silent Star also mentioned in Sarkareth's loot it could make sense for it to be a different star that fell to the Void.
But again, this is all based on existing lore- if there's anything new that affects this in Chronicles, I haven't seen it yet.