Why are there air vents if there is no HVAC duct?

When my good friend and I moved into our home, there was wall-to-wall carpeting in every room. The first thing my partner plus I had on our list of two dues, was unfastened the wall-to-wall carpeting plus every room however the guest room. The guests that my good friend and I got to our home, was usually our parents. His parents plus mine both liked wall-to-wall carpeting. When my good friend and I began ripping the carpeting out of the other rooms, I was surprised to see air vents in the floors. There were two air vents in the main dining room, plus two air vents in the dining room. I couldn’t understand why they were air vents if there was no HVAC duct in the house. My partner got a chuckle out of it, however I didn’t see anything funny about it. I had air vents in this attractive hardwood flooring my good friend and I had uncovered, plus they were necessary! All the air vents were doing was taking away from the beauty of my hardwood. After calling the Heating, Ventilation & A/C business, I called the flooring center. I wanted to see if they could cover that part of the flooring were the air vent was, plus make it look like it belonged in that area. The Heating, Ventilation & A/C business showed up before the flooring business. They told us this house originally had HVAC duct, however when the owners put in ductless Heating, Ventilation & A/C, they only had the HVAC duct unfastened plus closed off the air vents. This made me feel little better, however I still had to get rid of the air vents. The people from the flooring business assured me they could make it look just like the rest of the flooring, however it was going to be a little extravagant. Now I understood why they just closed off the air vents plus left the covers there.