On Page 59 of the Digi ZigBee SMT Manual (search for 90002002_M its the first PDF that comes up in my search window) it states:
Many-to-one routing is an optimization… Rather than require each device to do its
own route discovery, a single many-to-one broadcast transmission is sent from the data collector to establish
reverse routes on all devices.
Then in the next paragraph it states:
When a device sends data to a data collector, and it finds a many-to-one route in its routing table, it will
transmit the data without performing a route discovery. The many-to-one route request should be sent
periodically to update and refresh the reverse routes in the network.
So no its not a star typology at the physical layer that’s how WiFi and standard 802.15.4 (older xBee networks) work but it has the same benefits at the routing level reducing the route discovery traffic of a mesh only network. Its the best of both worlds you don’t have the single point of failure like you do with WiFi and it vastly reduces routing traffic since the routers simply past the packet on without the discovery overhead.
On the next page they illustrate how the routing works.
I was pointing out SmartThings is not a simply Mesh Routing AODV network they use many to one routing which is more like hub and spoke routing you would see in a star network.