Those sync.cache files are state files of the rsync backup uploader. That has to run as root to be able to list and read the app's files, the app file permissions here depend on the app itself and how it manages permissions.
The yellowtent user as such does not have root rights on the system and uses helper scripts in such cases. The list of scripts which need and thus run with elevated permissions can be found at https://git.cloudron.io/cloudron/box/-/blob/master/setup/start/sudoers
