California is not imposing anything on other states in this case (you're exactly right that that cannot be done). It is only mandating what has to happen if you want to sell a car in California. The companies are the ones that decide it is better to hit the "one size fits all" configuration for economic reasons than to offer different models in other states. CA has no control over what these corporations decide to do; it can only impose laws that affect cars sold in California.
Just as an aside, CA air is not all that great, but the efficacy of the law is not part of the question, only whether the constituation of the united states (and its enabling statutes and regulations) allow (and in fact protect) those efforts by states to control non-Federally-pre-empted areas of life and law within their own borders and that's an established fact. I've been involved in both constituational, and to a lesser extent, environmental law, and that's just the way it is. California can't say "you have to build cars with X" they can only say "if you want to sell cars in California, you have to have X on them." Any car company is free to build cars without X and sell them everywhere else in the world.
Likewise, what India and China do is not something we, or California, can control.