Joan would guess that the fact that being kind just comes naturally to him, rather than being a tactic toward some ulterior motive, is exactly why he surprised Sherlock. Sherlock is cynical about human nature, and it's very hard to be cynical in the smiling face of Ted Lasso.

"It will be nice to see Coach Beard again," she remarks. "The others, too. You have a great team." She glances at him. "Do they know I'm coming?"