...Or, an exercise of people's freedom to purchase space from BC transit?

Really, if there's an ad at a bus stop, what's it to you?  Whoever bought it figures they can make a living selling only to people who can read Chinese.  If they're right, you're not their target market; if they're wrong, they go out of business.  Either way, they're subsidizing your bus fare.

If you have a problem with that, then I guess you have a problem with a lot of things that are "too Asian".