It was pretty obvious for everybody that the "promotion" to Arrakis was a trap, including to Leto. They're never surprised the attack is coming, just that it's

It was pretty obvious for everybody that the "promotion" to Arrakis was a trap, including to Leto. They're never surprised the attack is coming, just that it's sooner and larger than expected. But he took it anyways, for duty and honor. So in this respect he did exactly the same thing as his father - turned his back to the bull while performing for his people. And like a generation earlier, the bull turned out to be closer than expected.