Max and the tag along moon

Max loves his grandpa. When they must say good-bye after a visit, Grandpa promises Max that the moon at Grandpa's house is the same moon that will follow him all the way home.

On that swervy-curvy car ride back to his house, Max watches as the moon tags along.

But when the sky darkens and the moon disappears behind clouds, he worries that it didn't follow him home after all.

Where did the moon go - and what about Grandpa's promise?