Watterson is known for not talking to journalists and being very private. In an age of Instagram, Twitter, Facebook, MySpace (that still exists, right?), and other social and broadcast media platforms Watterson has not gotten on board with just about any of that, it seems. Which makes Watterson's privacy that of a normal person from before the internet era.
Of note, while he says that the visual sophistication of Pixar blows him away he still would not let anyone animate Calvin & Hobbes. And that is absolutely the right decision.
There's the documentary Dear Mr. Watterson coming up in mid-November, after all.