I don't have experience in Kong Gateway but I looked into the documentation you posted. Even if there is an EXPOSE instruction in the DOCKERFILE, it does not open any port on your host machine. You need to specify it in the docker run command.

E.G.: docker run -d --rm -p 8000:8000 -p 8443:8443 -p 8001:8001 -p 8444:8444 kong-image

"docker run -it --rm kong-image kong version" is only for testing purposes, it returns the version for kong (you just get the output of the version in the console).

So EXPOSE in Dockerfile is for documentation purposes.