Well, most code can just pass around Temperature objects without dealing with any particular units. There's no opportunity to mix up units there.

When some code needs to actually get a number out, say for the purpose of logging, it's possible to screw up with either approach.

With the author's classes, you could do

  void printTemperature(DegCelsius temperature) {
    log("Temperature in Kelvin: %f", temperature.getDegrees());
  }

With this Temperate class, you could do

  void printTemperature(Temperature temperature) {
    log("Temperature in Kelvin: %f", temperature.getCelcius());
  }

As the author says, "wrong code should look wrong." I think both of these look pretty wrong.

With the author's code you can define a print() function inside each temperature class, so that there is no mixup of units during printing. Or let the class supply its suffix instead of hardcoding it in an external print() function. It might not be always possible to follow that technique, but in general, it is better (according to the article, and I agree) to retain as much information at compile time as possible.