Plenty of people and businesses have their own (DIY, etc) devices that need to use DNS. I mean it wouldn't really be the internet of things, if it didn't actually use the internet...
For instance, I own a .house domain that I use for a bunch of stuff that I've programmed. It would be a pain in the ass to go change that domain out. Now take that to next level and you're a business that's deployed a few thousand devices that need to call home.
I guess all this is to say - IoT doesn't just mean cheap botnet honeypot IP cameras. Take a look at https://www.balena.io/cloud for instance
It's dubious whether the Internet of Things was ever a good idea in any sense. Especially given how, famously, the "S" in "IoT" stands for security.
"Internet" in this context usually means IP, and in any case it should be restricted to a LAN. If you actually own the device changing the domain or IP should be trivial, I don't think this is what the article refers to.