My wife’s iPad Mini spontaneously locked itself. As far as we can remember this device has never had a passcode, which made unlocking it problematic. On a whim she entered her AppleID password and it unlocked! Does this make sense to anyone?
Isn’t there an option somewhere to use the Apple ID password for the device?
If there is, I can’t find it.
Edit: There is an option to enter a “custom alphanumeric passcode” instead of a 4- or 6-digit passcode (which I did not know about); maybe that got turned on somehow 
This is about unlocking iOS device activation lock with Apple ID. Maybe that lock got invoked somehow?
If I’m reading the support article correctly, she would have had to enter her AppleID and password to unlock Activation Lock. She only needed to enter the password.
Passcode was definitely turned on, which we cannot explain - she never turns on passcode on this device (at least not intentionally).