He knew quite a bit about Han Yi. After his advancement to the Golden Core, they worked together for some time. He knew that this mysterious senior brother didn't like to meddle in the affairs of the sect, always elusive.
Therefore, he wasn't worried about Han Yi seizing power or interfering in the management and decision-making of the sect.
Moreover, Han Yi had already advanced to the Spirit Transformation stage. With such a cultivation base, he would be a stabilizing force for the sect, not having the time to manage its affairs.
The reason Zhuge Wu You asked him to explain was, on the one hand, to acknowledge his position as the Sect Master due to his seniority in the sect, and on the other hand, to bridge the relationship between the sect and Han Yi. After all, more than sixty years had passed and naturally, feelings would somewhat dilute with time.