A Cathay Dragon Airbus A330-300, registration B-HLB performing flight KA-622 from Hong Kong to Hangzhou (China) with 219 passengers, was enroute at FL330 about 130nm east of Hong Kong when the crew reported an aft cargo smoke indication and returned to Hong Kong for a safe landing on runway 07L about 35 minutes later. Emergency services did not find any trace of fire, heat or smoke. A replacement A330-300 registration B-HLE reached Hangzhou with a delay of 4 hours. The occurrence aircraft resumed service after about 23 hours on the ground.