With the way sharding works I wouldn't be surprised if the whole thing was real but only affected an extremely small portion of the users, and in such a way that stuff that had been pushed into the mists of time made it back to the present somehow. That alone would qualify as a bug, the fact that facebook would shine the spotlight on old data like this is worrysome all by itself. If the data was private or in some other way hidden from normal view and suddenly given a much more prominent spot without the users being made aware of that ahead of time then that would be much more serious still.

For sure it seems that something changed.

The whole point of showing it next to a screenshot of the email or the message in the private inbox is to confirm that it is PRIVATE regardless of the actual content. There might be somebody out there who has an unusual interest in other people's private messages, but I think the vast majority of people are looking for something a bit more real than "this happened to me."

You're asking me to believe what other people say without any proof. I stopped doing that when I lost my religion.