The dependent typically goes on the Y axis. That said, he does seem to be going at it in a non-intuitive manner (for me, anyway). The cause and effect seem backwards. He's optimizing for a customization level even though that's clearly the cause for happiness, not the other way around.
Not disputing his point, but I agree, the graph is confusing.
Not disputing his point, but I agree, the graph is confusing.