I just noticed that I earned the "Excavator" badge a few minutes ago, putatively for a post that was "deleted or otherwise unavailable". So, apparently, did dozens of other people. I don't recall making any edits to old posts recently. What's going on?
There were some minor glitches in the intial awarding which caused people to earn multiple iterations of the badge (it's a one-time deal). Consequently, to handle this, we rolled out a fix that unawarded all of the badge instances, then re-awarded them afterwards. Getting the badge but having no associated question was probably an artifact from that process, but it is since no longer present.
You rightfully have the badge attributed to this post edit last month, which was to a year-old post. It was only awarded recently, rather than at the date of the fact, because the badge was only just introduced.