Yes, sorry, it makes full sense, because to know what information must be exported to the motion vectors pass, the plugin must extract and process all the motion blur information from the scene.
When you enable the motion vectors pass, the beauty rendering is done without MB to allow you to apply the MB in post, but the motion blur options must be enabled to let Octane extract and process all the motion data and build this motion vectors pass.
Hope it helps,
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini