I get the idea that Captain Wentworth is still resentful, is as anxious as Anne herself to avoid dancing with her (Anne counts down her 'safe' time as the longest she can go without being thrown into his company, and is relieved at her escapes), but can't help wanting to dance with her in a way, feels sorry for her having to sit out at the piano, confused as to whether he is expected to dance with her and indignant at the others for delegating her to the piano. Maybe he saw those tears?