It is likely that he set his move order before the battle was over. You can do that many, many hours before the battle ends and you will begin moving automatically.
Or he's a filthy liar, I dunno.
Thank you for this observation, it brings to light the fact he most likely set movement before the battle. This gives us two options. He set a movement point away from us before the battle, implying he never meant to stay around after his retreat to get his gear he needed oh so badly. Which leaves us with the second option. He knew of the plans to stay and fight, all the while our agreement still stood, making us rather lackluster on the recruiting for said "battle".
I guess this is a learning experience. We must give neckbeards the iron nails of the light spiked club. No exceptions, no compromise, no beard trimmers.