My understanding of the horning is, aside from just picking up the behaviour from others, they're trying to manage their environments. Compared to what happens on Chinese roads, people in other countries operate like precision teams - they obey lane conventions, they sit on the one speed limit, they stop at lights, they even indicate. Chinese driving, which is increasing in speed, is developing horn conventions instead.
And since it's more or less only horn conventions, and not anything else, they're stupid conventions. Like approaching from left rear and planning to both overtake and then turn in front of - that's horn time.
I think they do all this to positively avoid the creation of social institutions that grant other people right of way. Thus on the roads as in all other aspects of Chinese culture.