You can see the reason for the Horde's retreat (spaceships) from the Horde position. You see the randomly warp in and start shooting at the Horde immediately after, which explains why the Horde couldn't sound the horn in advance. The cinematic triggers just after they stop shooting. There's no duping here. Hatred? Sure. But the level of hatred to disregard data that was right in their faces would be so high a new Sha of Hatred would have spawned from it.