If you're going to be pedantic about minutae, you have to get it right.
The "image side of a Dockerfile" isn't a Dockerfile, it's an image, more specifically an image in the OCI Image Format [0]. A Dockerfile is just the most common syntax for controlling software that can create an OCI image (such as Docker and Podman).
You could argue that the OCI Image Format is declarative, but that's not relevant to OP's comment about Dockerfiles.
The "image side of a Dockerfile" isn't a Dockerfile, it's an image, more specifically an image in the OCI Image Format [0]. A Dockerfile is just the most common syntax for controlling software that can create an OCI image (such as Docker and Podman).
You could argue that the OCI Image Format is declarative, but that's not relevant to OP's comment about Dockerfiles.
[0] https://github.com/opencontainers/image-spec