I believe that this is something that could be better answered on the African Violet forum (the popular houseplants that can be easily rooted from leaf cuttings are quite different from true violets). While some sort of graft chimera is a possibility, it could also be that the two leaves rooting in such close proximity would eventually give the appearance of a single plant with two different flower colors. If leaves taken from such a plant and rooted separately developed into plants with only one of the two colors, the latter is most likely what actually happened. The African Violet forum would be an appropriate place to pose your question; otherwise, it might take experimentation on your part to get closer to the truth.