So for sshfs mostly we just do a local sshfs (fuse) mount point and then the backup strategy runs exactly the same way as for all other backup targets. So that code is not specific. However if you use rsync with hardlink support, then sshfs really can shine and for that we have added specific code paths to do the remote ssh login and create the hardlinks on the server directly, which is the most common operation for incremental backups. This speeds up the backup process a lot.
I am writing this, since above it seems to be about that optimized code path, which is doing the ssh login first and then runs the cp on the remote host (not your Cloudron).