When quizzed by Dr. Sit and others about how Ah Chu came to be injured by Shaolin's Mighty Gum Gwong Palms, Kiu Fung and Ah Chu told two different versions of the story.
Kiu Fung's was closer to the truth: he said that Ah Chu had been injured by a Shaolin monk, which was true. When the two Shaolin monks present at Tsui Yin Manor asked him about his recent raid at Shaolin and how he had abducted a Shaolin monk from the temple, Kiu Fung denied having done any such thing.
Now technically, Kiu Fung wasn't lying because he indeed abducted no Shaolin monk; the "Shaolin monk" he had taken from the temple was just Ah Chu in disguise. He knew what the two monks meant, however. In effect, then, Kiu Fung was telling a half-truth. Nothing he said was false, but he was withholding information that could have clarified everything. Kiu Fung doesn't lie, at least not as an adult. He admitted to Ah Chu that he had been quite a liar as a child, but he had never lied again after entering gongwu. But did he, in fact lie, to those two Shaolin monks at Tsui Yin Manor?
Ah Chu's lie is even more problematic: the way she described her attacker, it was clear that she was trying to get the people there to suspect Mo Yung F'uk. Of all people, why would Ah Chu tell lies that would hurt the reputation of her master? She had always been loyal to the Mo Yung Family before.
I understand that all this was done to get Dr. Sit to heal Ah Chu, but the lying that Kiu Fung and Ah Chu were doing seemed out of character for both of them.