That’s the smoking gun

The author thinks the same, hence why people can pay them 50 a month to get a non-anime version.

I think it was rsync indeed. Afaik rclone and rsync are different developers, despite the name

Just a FYI, when using a tool like rclone to backup data to some cloud, it can also encrypt the files for you when pushing data, and decrypt when pulling data. Of course, the files will still be unencrypted at rest.