A husband's sweet talking!
There were many people that attacked Kyoya, so he knew that it wouldn't go unnoticed. They also brought up a lot of treasures to deal with Kyoya that seemed unique to this 15th floor! All of this was valuable and some people might have seen Cero and his group going toward the 15th floor.
There also could be some rumors silently sweeping through Wings Free area and so the leader got the news.
'The worst case would be if the branch's leader came up to her.'
Kyoya knew that it would be the worst solely because he was just a friend and someone who benefited from the privileges of this strong party. For example, Kyoya knew about pyromaniacs' case from his house thanks to them and he never had to worry about his life, but things began to turn a little too wild.