I notice the article doesn't say whether the production of synthetic caffeine is inherently dangerous or polluting, merely that a major source occurs within a polluted/low-regulation place.

I don't see that coincidence--with one item it's not even a correlation--as very compelling. There are great many completely innocuous products or manufacturing steps which could also be located in a place like that for economic reasons.

So it seems another framing could fit: "Synthetic caffeine is so easy to manufacture and so compact to ship that there was a race to the bottom one price, and now it is concentrated somewhere with a very cheap labor costs."

Yes, the article never outlined the practical differences between natural and synthetic caffeine.

...there are none. you could argue residual solvent but FDA would not allow that, and depending on the industrial process this would be a concern with caffeine extracted from "natural" processes as well