Thermal cracking of Chloroethane produces Vinylchloride(chloroethene).
They mentioned Chloroethene because it's Industrially more important as compared to Chloroethane. You must remember it is obtained by thermal cracking of the initial product-chloroethane.
I don't think you really need to know how chloroethene is obtained.
You just need that chloroethene which is a derivative of ethene is an important compound used in PVC, which is very common in our lives.
That is one of the different uses of ethene. You should limit yourself to this for now
