While traditional Chinese virtues do underline the importance of modesty, the Chinese find out that when facing other nations, modesty is simply a lost virtue. Frankly, considering some of half-assed stuff the other nations have been toting around like life their greatest achievement, there is simply no reason for China to downplay anything we have actually done.
Also, humble is a religious term and sometimes implies just because a guy belong to a religion, he is somehow much justified in his action than others. Fortunately, Chinese are atheists.