CMMotionActivity in WatchOS 3: independent of iPhone?

Does CMMotionActivity in a WatchOS 3 app report Activity as per the Watch's sensors, or the iPhone's (iOS 10) sensors, or both?


The underlying problem is that a Watch user can be walking around the house when a symptom is experienced, while the iPhone is stationary on a desk. Also, knowing when the user transitioned from stationary to moving, or stood up, is important.