I think Hanlon's razor applies here. Sure, China could be nefarious and trying to sicken people in the west with their poop vegetables, but I'm fairly sure they all consume the poop vegetables themselves domestically as well. And I say vegetables because why would they stop this at garlic?

So its more about abject stupidity and the typically anti-human communist mindset where they would sicken the masses to save a couple bucks on the production of a thing. Until the wrong CCP party official eats it, gets sick, and then executes the CEOs of the industry as revenge.