The ideal knight was not a braggart. Medieval society as a whole, after all, was dominated by a religion in which the Savior himself was a humble man who preached that "the meek shall inherit the earth." The Church condemned both pride and displays of wealth and consumption. Indeed, pride was one of the seven deadly sins. That medieval knights often did not live up to this ideal goes without saying: chivalry was always the ideal, not reality. There would not have been so much preaching against excessive consumption and extravagant dress and pageantry if knights and noblemen had not commonly been guilty of engaging in all of it.
Balian’s humility can best be judged by the fact that despite being viewed by Arab chroniclers as “like a king” after Hattin, Christian accounts singularly fail to describe a man who was "lording it" over his fellows. Indeed, even the chronicles that detest him, such as the Itinerarium Peregrinorum et Gesta Regis Ricardi, attack him for other failings. They call him cruel, fickle and faithless -- all because he did not do Richard of England's bidding, but pursued his own policies. Yet they notably fail to allege that the man who was "like a king" (and step-father of the legitimate queen of Jerusalem) was excessively proud or haughty.
Obviously, the absence of allegations of pride does not prove humility either. Yet when one considers the fact that Ibelin was seen as virtually the only nobleman in the entire Kingdom of Jerusalem with stature and authority, it is remarkable that he never himself laid claim to a position of per-eminence. Conrad of Montferrat, for example, who put up a spirited and successful defense of Tyre, almost at once laid claim to a lordship he had not inherited, and later laid claim to the crown itself. He has also gone down in history as grasping, intriguing, selfish and excessively ambitious, as a man willing to cut almost any deal with Saladin for the sake of becoming King of Jerusalem.
Balian d'Ibelin in contrast acted consistently in cooperation with his fellow surviving barons, usually through the High Court, or at a minimum with prominent nobles such as Reginald de Sidon, the Tiberias brothers, and Pagan of Haifa. Given the fact that his eldest son later fought an entire war to defend the institution of the High Court of Jerusalem (i.e. the barons sitting collectively), it is fair to presume that Balian raised his son to respect this body and collective leadership instead of asserting one's individual rights. In the medieval context, that is a remarkable mark of humility.