Horton, who defeated London champion Sun on Saturday, confirmed remarks he had made to the Australian Associated Press (AAP) about tensions between the two during training.
"I used the word 'drug cheats' because he tested positive," he told reporters about the report that was published before Saturday's final.
Sun, sitting next to Horton at the media conference, served a three-month ban in 2014 after testing positive for a banned stimulant. He said China's sports programs were clean.
"On the competition stage, every athlete deserves to be respected and there's no need to use these sort of cheap tricks to affect each other," the 24-year-old Sun added.
Sun, who broke down in tears while talking to reporters after the race and became red-eyed again after the press conference, has suffered a number of setbacks since he won two gold medals at the London Games in 2012.
Sun Yang and Chinese swimming team's supporters condemn Horton's remark "unfair" and "disgraceful" on social media.
