A confirm page should be shown when restoring any kind of backup (space or site), to inform the user of exactly what is going to happen, and to allow them to back out.

Ideally, there would be one page for a space backup/export, which would identify the space key being restored (and whether the space already exists), and a note that it won't overwrite the rest of the site. A second confirm page would be displayed for site backups, which would clearly say that all existing content will be deleted, and the content and users from the backup will replace it.