Network 'broadcast' traffic doesn't require that it knows, or can even receive information, about the network it's on. It knows it own address, and then forms a broadcast that 'blasts' the rest of the network range locally. One way shot, not unlike some of our radio broadcasts sent into deep space.
This is the primary difference between TCP and UPD traffic, and is also one of the biggest benefits of using IPv6. IPv4 had APIPA, but that was inherently restricted due to being based on a non-routable IP range.
If the device does come across a switching device, the device will know enough to repeat the blast on the rest of interfaces that it has active, repeating the communication down the line.
What to do about it? Good question...I have a Windows 11 device that has an LG TV that 'added' itself to it via this tech, and I'm personally not a fan.
Protocols, by the way, are going to be Web Based (port 80, 443, etc) or completely custom in the wild end of the port range. Block em all, and let the CASB sort em out.
