Unable to access mounted dir from the host

[koichirose]

Following the readme here, I created this docker-compose.restore.yml file:

services:
  borgmatic:
    container_name: borg-restore
    cap_add:
      - SYS_ADMIN
    volumes:
      - /tmp/borg:/restore
    security_opt:
      - apparmor:unconfined
      - label:disable
    devices:
      - /dev/fuse:/dev/fuse
    command: /bin/sh

Then I run:
docker compose -f $HOME/docker/borgmatic/docker-compose.yml -f $HOME/docker/borgmatic/docker-compose.restore.yml run --rm borgmatic

And I run this inside the container:
borg mount --remote-path=borg1 [email protected]:myrepo /restore (repo is at rsync.net)

I can browse /restore from within the container, but /tmp/borg on the host contains 0 files. I also tried different dirs in my host.
What am I missing?