It looks like you are referencing video analytics rules. To clarify, a Ground Zone does not exclude all activity outside of it, it defines a zone which the camera expects as the ground, and movement just above that can still be interpreted as occurring on that ground zone where people would be walking/driving. This can happen with sidewalks/roads near the ground zone.
If you are noticing unwanted alerts, first try shrinking the ground zone back away from the area where unwanted alerts occur, which should limit activity detection.