The relative rotation is the same, but since the cube (and therefor the system) rotates, the absolute rotation is different. Since FindLookAtRotation only uses location, it provides absolute rotation.
Notice how you have actually rotated throughout the clip. At the start you’re looking to the left of that wall, and by the end you’re looking to the left of a wall perpendicular to the first. This wouldn’t be possible if you hadn’t rotated.