This seems to me like a potential security issue.
It's neat, but not this dystopian neat.
I had no idea a Thunderbolt hub could serve as a parallel Ethernet hub, nor that there were devices that could or would want to take advantage of this.
But my Dell P2423DE monitor has a USB-C “dock” built into it so that I plug a single cable into my laptop which connects it to 2x 1440p monitors, power, mouse, headset receiver, keyboard and a wired ethernet connection.
Quite frankly, it’s awesomely convenient.
It’s totally legitimate to have a network port on a monitor.
This is for advertising plain and simple (and probably selling user data to some extent). That's direct income for the manufacturers so they care about it a lot.
This has exploit potential. If a properly crafted ad can successful take over a monitor, the attacker now owns a USB-C device with an Internet connection. From there, it can make the device pretend to be some other USB device, such as a keyboard, mouse, and USB storage. From that point, they can do almost anything.
In other words, they not hubs (or switches) in the Ethernet sense, just a different physical connection to an otherwise ordinary PCIe NIC.
I imagine non-Thunderbolt USB docks are similar, presenting as a USB hub with a garden-variety USB Ethernet controller attached to one of its ports.
With that said, I imagine a "smart monitor" with integrated dock would additionally include Ethernet switch-like functionality, to enable sharing of a single physical Ethernet port (or wireless connection) between the connected host and the smart TV subsystem, just as some servers allow sharing of a single Ethernet port between the installed OS and an onboard BMC.
(Insert sarcasm here.) /s