If someone deleted their own post you get the message: (post withdrawn by author, will be automatically deleted in 24 hours unless flagged). But you can still see the original message in the edit history. Shouldn’t that only be for admins?
In my opinion, no, it’s fine for everybody to be able to see it. If you have sensitive data in there, you should flag for an admin to delete the post immediately.
The grace period there is to help prevent griefing, by giving a period where people can flag the post to prevent its deletion.
This is by design. If you are uncomfortable about letting users see post history there is a separate setting for it.