As Chi Songzi was an ancient celestial, he could predict and estimate very well. Hence, it was not surprising for him to know about Shen Lian. The reason why Shen Lian raised this question was that he knew that Chi Songzi did not know about him through prediction.
Shen Lian was so certain over this matter because he had obtained profuse attainments. Those who have reached the state of holy deities would be able to be informed about antecedents and deduce future outcomes through prediction. Although this was not a difficult technique, there was a point which could not be neglected. That is if you were predicting about someone who was compatible with yourself, he might realize about your prediction. Even if he was not able to determine who was the one predicting, he would be alarmed.
However, Shen Lian was not alarmed this time around.