Putting aside the matter of him possibly leaving again due to work, I'm sure that Piano event flyer has Ri-chan written all over it in his mind.
I like that TL note. The "-kun" honorific when used on a junior in this manner, can also be used by bosses on female subordinates or teachers on female students. It's not limited to e.g. a girl calling a boy her age like we usually see in manga/anime.