Glad it went ok. I think you reacted with good composure and insured the situation didn't escalate.
You were definitely in violation of both your concealed carry permit and SC law for carrying a handgun in a vehicle, as the item was neither concealed nor "about your person" as defined by the law. It must be both to be legal for concealed carry. And "about your person" (notice it is not written "on or about your person" as you wrote in your post) means essentially attached to your body (in your pocket, hand, waistband, holster, etc.). If you aren't carrying the weapon, it must be in a closed glove or in the trunk. I suspect you pulled that language from a paraphrased version on a non-official website.
Of course the gun can be loaded or unloaded as there are no prohibitions in the law requiring an unloaded weapon in the car. I'm glad the LEO let you go!
LINK TO FIREARMS LAW: Link Removed
More on carrying in a vehicle in general:
SECTION 16-23-20. Unlawful carrying of handgun; exceptions.
(9) a person in a vehicle if the handgun is secured in a closed glove compartment, closed console, closed trunk, or in a closed container secured by an integral fastener and transported in the luggage compartment of the vehicle; however, this item is not violated if the glove compartment, console, or trunk is opened in the presence of a law enforcement officer for the sole purpose of retrieving a driver’s license, registration, or proof of insurance;
SECTION 16-23-10. Definitions. (PROVES THAT YOU CAN THROW YOUR GUN IN THE BACK OF THE FORD EXPEDITION, ETC., AS LONG AS IT IS "in a closed container secured by an integral fastener")
(10) “Luggage compartment” means the trunk of a motor vehicle which has a trunk; however, with respect to a motor vehicle which does not have a trunk, the term “luggage compartment” refers to the area of the motor vehicle in which the manufacturer designed that luggage be carried or to the area of the motor vehicle in which luggage is customarily carried. In a station wagon, van, hatchback vehicle, or sport utility vehicle, the term “luggage compartment” refers to the area behind, but not under, the rearmost seat. In a truck, the term “ luggage compartment” refers to the area behind the rearmost seat, but not under the front seat.
LINK TO CONCEALED CARRY LAW: Link Removed