The difference between “things with computers in them” and IoT devices, as I see, is that the IoT device needs to be smart about the environment it inhabits and the context of how it inhabits that environment.
A thermostat adjusts the temperature.
A smart thermostat can adjust the temperature a little more efficiently from your smartphone.
An IoT thermostat is aware, on a fundamental level, “I am a thermostat” and can reason, in a meaningful way, what adjusting the temperature by five degrees down in the afternoon on a sunny day means and versus adjusting the temperature five degrees down at 4AM in the morning in the dead of winter actually means to instead.
It goes beyond some fuzzy logic with an historical record and becomes a new way to work with available data, usage patterns, and the interactions that humans and other IoT devices have with itself.