I looked up South Carolina and it looks like idling the engine applies only to commercial vehicles.
Follow that concept...
Reassuring . . . NOT!
I also had a look and came up with these links:
http://www.scstatehouse.gov/code/t56c035.php
http://www.arcticbreeze-truckac.com/content/no-idle.html#NO
Both of those apply to diesel trucks, probably the same as you found.
I can’t find any link where is says you can’t warm up your car in SC. Therefore I don’t understand the reference to SC in the second paragraph of the article.