It's possible there was an error in processing the chillies. Leaving too much skin on can make for a "soapy? taste. Or, if chocolate has been alkalized (Dutched), it can be too alkaline, and that risks a reaction that produces a soapy flavor. Some of the chemistry is very like making soap, and it takes care to see that it's not over done so that it literally becomes soap.
On the other hand, from a U.S. perspective, Mexico has some peculiar tastes in candy. It can be difficult to believe some of it is accepted as candy. I once bought a big bag or Mexican hard candy at a flea market where little English is spoken. It looked like any other hard fruit flavored round candies. The taste was very far from what we think of as candy. Horrible kind of describes it. I ended up leaving a big bowl of it on my desk. No one hit it twice. Very useful for dealing with the more obnoxious sort of children, too.
