I believe it uses the outside temp to determine what it will do. I'm pretty sure it defaults to using the defrost and puts it on full blast. I know that as soon as I get in and turn the key it goes to my previous setting, but it's totally different when the remote start is active. I had an 07 Saturn with the factory start and it would turn on the rear defroster, heated mirrors, and the main defrost it was the best thing about the car. I assume the truck it pretty much the same I just don't have the rear defrost in the truck.
2009 Silverado Z71, 5.3 V8, HD towpackage.