Even though Qin Dongxue tried to cover up as much as she could with words like predict and guess, Ling Yun knew that Cui Lao must have contacted her before. It seemed like Qin Dongxue didn't want to tell that to Ling Yun personally.
This was indeed the truth. From Cui Lao's perspective, Qin Dongxue was Ling Yun's only elder now that Qin Qiuyue wasn't around. Cui Lao's trip here to meet Ling Yun was to tell him about his true identity and to bring him back to Beijing's Ling Family to meet Ling Lie. If he were to hide this from Qin Dongxue and tell Ling Yun the truth behind her back, it wouldn't be nice.
Without mentioning the fact that the Qin Family wasn't any weaker than the Ling Family… even if Ling Yun was with an ordinary family, he should still gain the approval of the family before bringing him back to acknowledge his biological family.