A recent update about Tai Shan (who shares a birthday with Callum) says:
Among the panda staff, Tai has a new set of nicknames and descriptions, like “little toad,” “little monster,” “wild man,” and “rotten child,” just to name a few. When he is awake, if he is not chewing or climbing on Mei to get her to play, he is trying to “help” the keepers move bamboo. A new soccer ball will provide some distraction so that the keepers can finish the task.
Hm… maybe Callum and Tai share traits other than their birthdays.