I have seen the AI do very strange things moving armies.

During an Aragon game, The Almohads were cornered in Granada through having a civil War... The Kalifah attacked Morroco and besieged the rebels. I moved in from Cordoba, a message appeared The Almohads have decided they cannot win the battle and are retreating.

Now the Almohads had no Navy, and I had captured Morocco and besieged the Rebels myself, but the Kalifah was not in Granada because I could see everything thanks to my agents... He couldn't have ventured east because Algeria was also Rebel at the time.

How did his vast army escape, and how come I didn't get a ransom or a notification of his capture?

The Mystery of the teleporting Monarch