No, it’s not your fault. Github does not support downloading a subfolder. You have to download the entire package (see the ‘Download Zip File’ button on the lower right corner of this page: https://github.com/rayshobby/opensprinkler) and unzip it, then go into the subfolders and find the updater program there (in Mac, just find the osFirmwareUpdater.app which you saw, and then run it).