Run kubectl inside a cluster

Does this mean, that kubectl detected it is running inside a cluster and is automatically connecting to that one?

Yes, it used the KUBERNETES_SERVICE_PORT and KUBERNETES_SERVICE_HOST envvars to locate the API server, and the credential in the auto-injected /var/run/secrets/kubernetes.io/serviceaccount/token file to authenticate itself.

How do I allow the serviceaccount to list the pods?

That depends on the authorization mode you are using. If you are using RBAC (which is typical), you can grant permissions to that service account by creating RoleBinding or ClusterRoleBinding objects.

See https://kubernetes.io/docs/reference/access-authn-authz/rbac/#service-account-permissions for more information.

I believe helm requires extensive permissions (essentially superuser on the cluster). The first step would be to determine what service account helm was running with (check the serviceAccountName in the helm pods). Then, to grant superuser permissions to that service account, run:

kubectl create clusterrolebinding helm-superuser \
  --clusterrole=cluster-admin \
  --serviceaccount=$SERVICEACCOUNT_NAMESPACE:$SERVICEACCOUNT_NAME