That means they are not "demo" vehicles, but were titled to some end user consumer before. A car can have miles and be sold as "NEW" provided it was never titled to anyone. Demo cars generally are not titled to anyone, so are sold as NEW.
What both of those cars likely are, are cars that were sold to someone, then returned for some reason, THEN turned into demo cars for the dealership.
So, if the car has extremely low miles like that, but is being sold as used, you can guarantee that it was titled to someone (meaning sold to someone) then returned.