He didn't say his IoT devices relied on 'cloud' accounts. He said there are IoT that use services on this domain.

Imagine he's set up some IoT devices at his parents' home, and those devices use services that he hosts somewhere on the internet. It would be silly to hard code the IP addresses in there, right (unless he operates his own ASN)? So he would use DNS to allow those devices to find his server(s). This would be the case whether the servers are at his home, at his office, or in a rack at a data centre.