YAML isn’t the DSL, it’s just the language used to express declarative config because the tooling is ubiquitous and it’s rare that anyone uses it as anything more than a nicer version of JSON.
For Kubernetes, it’s CRDs that are written in YAML and they conform to a specification.
YAML may be a known syntax, but the use of it still requires domain specific knowledge, and is still a domain specific language expressing those domain specific concepts, as to what the expected keys and values are allowed to be and how they are interpreted.