The title is a bit misleading because we are only talking about two very niche Hershey products. Special Dark and 85 percent cocao bars. Some people ITT seem to make the leap that it's the iconic milk chocolate bar.

Which makes sense, since that (the darkest varieties) is a less processed chocolate. Also, it being done in Africa, a place where leaded gas is still being used (until recently), means that it was likely absorbing it through the air as they dried out the beans.

https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.8009#:~:text=Because%20of%20the%20high%20capacity,unshelled%20beans%20at%20cocoa%20farms.