I have received the following, slightly premature, notification.
I don't have the required score, nor do I have access to the moderator tools (so far as I can see) — just the notification.
As Chris said above in comments, it's probably just unlucky that the script caught your rep >= 10k and then a vote was removed in the time you were away from the site.
But at the same time, I don't understand why the system doesn't do a final check when the notification is due to be delivered. I would think it's easy enough to figure out if the message doesn't apply, and unflag the privilege so you can get the notification at the proper time. Maybe it's too expensive a process.
I suppose we could forget the database part and deliver a different message instead.
You did have more than 10k reputation -- but your reputation decreased, because someone either unaccepted one of your answers, performed an undo of an upvote on one of your posts, etc, etc.
I don't think this is common enough to warrant a whole set of code to prevent it; every new line of code is a potential new bug.