You are correct!
The Motion driver is the legacy driver that many users have installed since before and make use of the standard Zigbee clusters. It uses a counter for resetting the alarm efter an initial motion detection.
The Occupancy driver makes use of the Philips Hue Manufacturerspecific Zigbee cluster enabling support for the device to enable/disable the alarm based on movement and absence of movement.
Installing a new device I advice to use the occupancy driver.
