It depends on how you look at it. They were stored online (Dropbox servers) as well as locally (Macbook). The problem is that a bug in Dropbox's client turned a de-sync operation into a delete operation. So one way to see it is that even having local storage was not safe because the sync was flawed. Another possible way to look at it is if your only local copy is synced with the cloud, then effectively your only storage is online.