Reader, Michelle Sunde, interpreted the scene as this:
"Just before he shoots the choir, he dances to their music. I took that as a nod to cultural appropriation, where people will take the bits of black culture they find amusing and exploit it but don’t give it its due credit or appreciation. Then, when he tires of the choir, that’s when he shoots them. He’s used them for what he can get from them, then just as quickly, and with complete disregard for their humanity, he dismisses them."