Carlos doesn't know if he's surprised or not. Probably not, since everyone seems to want to talk to him about Cecil these days. But something tells Carlos that Joan isn't here to ask highly personal questions about things Carlos really doesn't want to discuss with the general public. Her tone was far too businesslike for that.

So his tone when he asks "What is it?" isn't nearly as snappish or weary as his tone has been known to get. It's concerned, and sad, but not hostile.