"There are so many troublesome people around you." This phrase of the cardinal is like a pouting. He is saying this because he could never have a decent talk with MC. As a person pursuing knowledge and truth of the world, MC is like his researched hamster and also a smart person to discuss stuff that no one wanted to discuss as they think he was too devoted and feel annoyed by his obsession with knowledge (or maybe because she's a good listener). MC never told a lie and she can pique his curiosity. She took his words by heart, and he wanted her to remember as this is his "goodwill" for her sincerity around him. At least she still respect him and treated him as anybody should to a cardinal, not a young genius cardinal.