Isn't there a saying that when the stars came down, the words cursing Qin Shihuang were engraved on them, so Qin Huang killed everyone who saw the stars. In fact, it was Qin Huang who discovered that Tianxing had the ability to create weightless space and tried to hide the secret, killing many people. Qin Huang wanted to move the stars to Huangling, so he moved to Huangling ~ Yi Xiaochuan also said that Qin Huang hoped to build a heavenly palace with the stars.

As for how Lao Cui got the powder ... there are too many possibilities ... there is no specific explanation in the TV series

I think it may be that there is star powder in the pit left by the meteorite hitting the ground. ...