I feel Barristan, both in the books and so far in the series, has been more of a Hand than a mere queensguard to Dany. Aerys had plenty of people in his court, and he was a young knight among many, while Dany is a green queen surrounded by strangers. Sure, in the books he doesn't usually say what's in his mind without being asked to, but it doesn't strike me as too out-of-character his shock to Dany's trade of a dragon.