Cal has his doubts, but he is not here to criticize how Sherlock sits. Criticism is kind of the opposite of relaxing. He just mentally chalks it up as being a Sherlock thing (that's become an actual list in his head as of late, beginning at around the time he stopped thinking Sherlock Holmes? Really?) and turns his attention to the movie.

Or, most of it. It doesn't exactly require intense focus, and he isn't going to insist on sitting through the whole thing if Sherlock really does seem bored.