iPad screen is upside down, and says locked, try again in 3 hours

Most of the responses on this topic already posted state this is due to inputting an incorrect passcode too many times. But this happened on my iPad completely random. I used my iPad early this morning with no issue, and closed it up (just like I have for years now) so I could work in my office. Several hours later I needed to use my iPad, opened up the case, and this message was on the screen. I've had it with me all day so there is no possibility that access was attempted by anyone else. This was just completely random.

Why would my iPad lock itself up like this on its own?