The paper isn’t clear about this, but the crescent in that image is the moon, AFAIU. They’re using it as a baseline for luminosity of the UAPs, which are the mu

The paper isn’t clear about this, but the crescent in that image is the moon, AFAIU. They’re using it as a baseline for luminosity of the UAPs, which are the multiple (less bright) white speckles in the image.