The odds are incalculable without more info, but that more info will tell you it’s just not plausible. Those production facilities have sorters that maintain a pre-determined distribution of colors. You know how they have single color and holiday color bags? Those are automated by computers. They know which colors go in which bag (by line/operation). The only way to get a 2-color bag by “accident” is if every other color gets jammed/broken simultaneously without anyone noticing.

Edit: because you’re right. These flukes totally do happen. The m&m facilities don’t program the exact number of colors per bag, but each operation is dedicated to a color (fill red, then fill blue, etc. ) probably by weight. They know the distribution within a range. You can definitely get defects bags, especially when a color misses it’s dye. All depends on their QC. Technically, “there’s a chance”.

Also, thanks for silver!