Google Sites now allows multiple file uploads all at the same time, not one-by-one. With this update the method to view and download files also changes and the way Google Sites stores the uploaded file names.
Upload Multiple FilesNavigate to the page where you want to attach the filesUse the Add files link at the bottom of the page to open your web browser's file chooser.
Choose the file, or files, you want to upload. You can choose multiple files to upload in two ways: