There's no way to know what that icon really indicates. It could just be that the computer has commanded the battery heater to turn on, and not actual confirmation that the relay has actual closed, voltage is present, current is flowing, and the heater is actually heating.
But yeah, if the icon isn't there, it sure begs the question, "why?"
There is definitely no battery heater icon on the iPhone app on my phone and I do preheat my car at least once a week. I know what this icon looks like. I just always assumed because I’m an early build I don’t have this “feature” whatever it is.