I can try to answer to my best knowledge. Though, I am not sure why you ask whether concepts are written in GO.
I doubt it. Especially extensions have a free choise to use whatever they see fit.
Dockerfiles are not written in go. Though, the implementation that docker did/uses is written in go. There are plenty of tools that can generate an OCI compliant container image based on a Dockerfile - they don’t necessarily have to be written in go.
v1 is implemented in python (originally it was a third party solution, that become integrated into the docker portfolio), v2 is implemented in go.
The docker engine is implemented in go. Note: it still delegates operations to kernel features and linux libraries
Why would a concept be written in a programming language?