I don't know if that's necessarily the whole story.
Boutique chocolates tend to contain more cocoa solids and cocoa butter. Larger companies tend not to use as much and instead have fillers like palm oil.
It's then no surprise that a boutique dark chocolate might have more contaminants than mass-produced milk or dark chocolate.
So then compare to the mass produced dark chocolate that doesn't have filers. There's tons of it, just plain dark chocolate chips. (As opposed to a candy bar.)
Boutique chocolates tend to contain more cocoa solids and cocoa butter. Larger companies tend not to use as much and instead have fillers like palm oil.
It's then no surprise that a boutique dark chocolate might have more contaminants than mass-produced milk or dark chocolate.