The activation lock screen shows an obscured email address. Does that look familiar to either you or the person who now has the iPad? If not, then it's possible that someone cloned the serial number for your device and got that locked to a different iCloud account. This has happened with iOS devices and caused owners to become locked out of their devices, but it's not Apple disabling the device as part of some conspiracy.
If you have proof of original purchase from when the device was new, Apple will remove the activation lock for you, regardless of whether it's your iCloud account locking the device or someone else's.