Maybe he was wrong earlier.
If he thinks clearly it would be him that knows how persistent that guy could get when it comes to Shao Rong even compared to Shao Rong herself.
Though Ren Weimin never knew of him or his existence, from Zeng Yimo's perspective, it was always a direct challenge between Ren Weimin and Zeng Yimo himself.
Everytime Ren Weimin took a step towards Shao Rong, it was always Zeng Yimo that covered her traces perfectly.
Shao Rong doesn't want to know every little detail about Ren Weimin as she was scared that she would miss him the more she would know about him.
Hence she had long ago ordered Zeng Yimo about how to keep Ren Weimin away from her at all times and also to never tell her any details even if something actually happened that is related to him.
Zeng Yimo of course followed her orders and did what she told him to.
Hence he knows about Ren Weimin more than what Shao Rong herself knows about him.