Not Really an IoT Problem, Though
... and the "smartness" problem is more about the connection between the thermostat and the smoke detector.
Inter-connectedness between smoke detectors is not a new feature -- First Alert had it for one of their models. And Nest's "speak, don't beep" feature is nice but not really revolutionary.
But the connection with the thermostat is clearly an issue here. As the article states, affecting the air circulation can be a big deal, and this is especially true if you live in places that can get very cold.
Smoke detectors occasionally fail. This is not surprising, and if the smoke detectors were the only Nest product the author had, it wouldn't even be worth an article -- aside from complaining about the expense.