The correct answer to this open question is the following.
The symbol of the mamool cookies in the story is this.
The mamool cookies is a reference for the diversity of humanity. The cookies were made of the same powderer sugar. It covered all the cookies. So she said that every human being was similar. No matter if they had different nationalities or color of skin, as was the case of the story. One individual from Argentina who was the traveler, one from Lareado who was the lovely woman, or the mother who was from California.
The metaphor is that there is no better cookies. All of them are exactly the same. So humans have to understad and respect each other the way they are.