Lin Ze doesn't know how he reached the river where his feet sent him. This is the river where Meng Xing told him that his friend had gone missing and one of the places where he and Meng Xing had been. Lin Ze's subconscious mind which is the only thing that currently works in his brain still wanted to look for Meng Xing's friend, so he is here now.
He wanted to think that Qiu Qi was just lying to him. After all, the people of Huichen seemed to be hostile to him, and his confrontation with Qiu Yi before is proof of that. But, he knows that Huichen will never let their feelings or personal interests affect their business. So, Lin Ze knows that Qiu Qi didn't lie to him.