To make it even more clear and to take an analogy, you can talk about Maven but in reality the full name is Apache Maven (because Apache is the forge).
For Cristal it’s the same, you can talk about Cristal but the real name is XWiki Cristal. This is true even before this proposal, and for all contrib projects. They all belong to the XWiki forge.
You can also see this in Cristal code, for example: import type { WikiConfig } from "@xwiki/cristal-api";
So to conclude:
- Cristal can be deployed independently of XS
- But Cristal has a relation to XWiki, it’s an XWiki project (and thus its full name is XWiki Cristal)