Matze0211 is right, the Aeotec stick together with OpenHAB acts as a Z-Wave hub. You need to “include” your Z-Wave devices to the stick (which acts as a “controller” in the Z-Wave network). Every included device can then be made into a “thing” in OpenHAB.
Z-Wave can manage two controllers in a network, where one is a primary controller and the other one is a secondary controller. In theory that could be a way to include Z-Wave hubs into the OpenHAB universe. However, I did not stumble over any documentation where someone implemented/used that feature.
In addition to that, Z-Wave devices always belong to exactly one Z-Wave network (in the situation mentioned above it would be the network of the primary controller) and thus cannot be made available in another Z-Wave network.
Including a Z-Wave hub in parallel to a Z-Wave controller in OpenHAB is therefore most likely to be done via WiFi or network cable, if needed at all.