Most likely this is a multi-channel device. That is, it only has one z-wave radio in it and therefore only shows up as one device to controllers, but has two different relays (channels) that control power.
There are some people who are working on multi-channel device types (here’s a thread with some discussion on it: Zwave Power Strip from AEON), but I don’t know if this would work reliably with this device or not.