gitlab runner using wrong docker image for build container

I set up an gitlab-ci-multi-runner on my VM.
In the build process I provide an docker container with all the dependencies. But when I run it, the runner uses a different (wrong) docker image for his build container.
The messages look like that:

Running with gitlab-ci-multi-runner 9.2.1 (f0xxxx4)
on runnerVM (f5xxxxf0)
Using Docker executor with image docker.com/xxx/xxx/docker-build:stable ...
Using docker image sha256:fe32xxx...xxxa63c for predefined container...
Pulling docker image docker.com/xxx/xxx/docker-build:stable ...
Using docker image docker.com/xxx/xxx/docker-build:stable ID=sha256:9608xxx...xxxdf09 for build container...

Can someone tell me why the runner uses a different docker image for build container?
Why is it not taking the predefined container (because that's the right one...)

Here you can see my gitlab-ci.yml:

image: docker.com/xxx/xxx/docker-build:stable

before_script:
  - echo "Before script"


after_script:
  - echo "After Script"

stages:
  - build
  - test
  - deploy

build_release:
  stage: build
  script:
    - sudo make all BUILD_TYPE=Release
  only:
    - master
  tags:
    - tag1

build_debug:
  stage: build
  script:
    - sudo make all BUILD_TYPE=Debug
  only:
    - develop
    - runner-test
  tags:
    - tag1
    - tag2