Edit > Keyboard Shortcuts... and check the set you are using.
I've scrolled through the entire set and cannot seem to find what I'm looking for. The only thing that comes close is in the Product Area > File Menu > Revert at the beginning but this shortcut is [none defined].
Then it would be pretty much impossible for you to have reverted by using the keyboard. Could you have hit the menu item accidentally? Or opened a previous version?
There have been reports of cases where ID isn't actually saving when you use the save command, too.
It happened exactly as I described with the keyboard shortcut. Not sure how it's possible but it happened. I was going for ctrl + z for undo (working on a pc that's the short cut i made) and the revert to previously saved popped up. It's happened a few other times only in the past couple days. I didn't know if it was a weird update adobe may have done.
I've gone ahead and changed the Product Area > File Menu > Revert > [none defined] shortcut to something very complicated just to see if that does anything.
Maybe it was a fluke occurrence. We'll see.