Being a former Wendy's employee, I know the process of making the chili. The chili does no come precooked, or pre-made.
There is no way the finger came from the meat, because the raw meat is cooked, then boiled to remove excess grease, and then chopped to roughly the size of a dime.
There is no way (in my mind at least) that it came from the bagged vegetables (which consists of white onions and green peppers) because it would be highly visible and I don't see how it could pass through the manufacturer and then slip the cooks attention.
There is no way it came from the chili base, which is a powder and the first thing mixed in with water, the goal is to get even the smallest "clump" out, and 1 1/2 inches is a mighty big clump.
And that brings me to the last ingredient(s), beans, there are red beans and kidney beans, each in their separate cans. The cans are opened up, dumped into a colander and washed to remove excess "juice." In my mind this is the only ingredient the finger could have come from. It could have been well concealed, and depending on the fingers skin tone, blended right in with the beans.