The difference between running a docker image form a runner or directly

GitLab CI/CD
1

I know this was already asked here Difference between local Docker container and Gitlab Runner Docker container but now answer provided.

I need a customized maven docker image to execute my tests.
It requires me to tweak the time zone and add true type fonts.
I created my own maven image FROM maven:3.6.3-openjdk-8

I am using the gitlab/gitlab-ce:latest locally on my mac and executing my tests in two ways

  1. from the container shell

    docker run -it -v /Users/myuser/.m2:/root/.m2 -v \
    /local/config:/local/ config -v \
    /Users/ myuser /workspace/:/build \
    –network=mynetwrok \
    maven- tweak:1.0.1 bash

  2. from the local gitlab with the following runner config
    oncurrent = 1
    check_interval = 0

     [session_server]
   session_timeout = 1800

 [[runners]]
   name = "maven- tweak "
   url = "http://gitlab"
   token = "xyz"
   executor = "docker"
   [runners.custom_build_dir]
   [runners.docker]
     tls_verify = false
     image = "maven- tweak:1.0.0"
     privileged = false
     disable_entrypoint_overwrite = false
     oom_kill_disable = false
     disable_cache = false
     volumes = ["/cache","/Users/myuser/.m2:/root/.m2", "/Users/myuser/workspace/:/build "]
     network_mode = "mynetwork"
     shm_size = 0
   [runners.cache]
     [runners.cache.s3]
     [runners.cache.gcs]

I am trying to figure it out for a while now.
What are the deferences between the two executions so I could figure out the problem