I'm with Manzabar. Over the years I have learned several things about web hosts and one of them is this:
1. The crappy ones don't backup your site at all.
2. The better ones actually do backup your site, but not all that often. Plus, they will restore a backup at will without telling you. All of a sudden your site is 3 days behind where it was a moment ago. Still better than host type #1.
3. The best ones backup your site daily and incrementally. Then, if they have to restore it, they restore only the increments required. Thus, the fact that a restore has been done is (most of the time) invisible to you. The best of a bad set of option.
So, I think you have a #2 type of host who is in the habit of restoring several day old backups when something goes wrong. I would recommend checking your hosts website for something like a 'network status' page. You may be able to read what has happened over the last few days and see that indeed a server went down and a backup was restored.