Deleteing pods/deployment does not delete docker's containers. Why?

I have deleted all PODs:
kubectl delete pod {pod_name}

I have deleted all Deplyments:
kubectl delete deployments {deployment_name}

Why do I still see running containers that Kubernetes created for these PODs/Deployments?

user1@user:~$ docker ps
CONTAINER ID        IMAGE                                 COMMAND                  CREATED             STATUS              PORTS                                                                                                      NAMES
a8427505af0d        nginx                                 "/docker-entrypoint.…"   7 days ago          Up 7 days >80/tcp                                                                                         mynginx
74d84fd550c8   "/usr/local/bin/entr…"   2 weeks ago         Up 9 days >22/tcp,>2376/tcp,>5000/tcp,>8443/tcp   minikube

I think I understand that only now and this is what @stephendotcarter was once trying to explain me in other post.

Because I am using MiniKube, there is minikube docker container that acts as a kind of Worker node.
All docker containers are to be deployed INSIDE that one container.