I run the official PPA version on Ubuntu 22.x. I mount the drive containing backups to /backups and it is BTRFS compressed zstd.
I have noticed this issue when I am doing 2 image backups same time. The second computer somehow manages to end up in /backups folder of internal boot (small SSD) volume creating serious risk. I really don’t know how is it even possible.
sudo findmnt output:
├─/backups /dev/sdb2 btrfs rw,nosuid,nodev,relatime,comp