Banning the ad - in which the decision has been reversed, and it was entirely in their right to pick and choose which ads they wanted to display - is a far cry from homophobia, is it not? You should go to some more conservative countries in Africa, Middle East, or Asia, or even some more conservative neighborhoods in the US or Europe to see what real homophobia is like.
Hong Kong society in general are actually pretty neutral on this topic - they just don't like it when it is constantly being shoved down their throats, or when the LGBT community screams and screams intolerance and injustice at the slightest inconvenience - all the while when society is battling issues of serious human rights (extradition law), judicial independence and a rapidly declining quality of life.