That's weird -- the concept of "root directory" is defined to a bucket. There is no "root dir" in S3, is there? It's only within a bucket itself.
And since the documentation states:

If we have a remote file

then StorageManager.download_folder(‘

’, ‘~/folder/’) will create ~/folder/sub/file.ext

Then I would have expected the same outcome from MinIO as I do with S3, or Azure, or any other blob container