I'm not sure but they look like chemical burn from overspray. Did anyone spray fertilizer or any sort of chemical nearby on a breezy day? Some plants are hyper sensitive to common chemicals and just a tiny dot of it will burn the leaves. The way it is evenly sprinkled throughout the collards and spinach below makes me think it is something chemical and not a virus. There isn't a whole lot you can do except wait and see if it gets any worse. If it starts spreading and weakening the whole plant I would yank that plant out of the garden and throw it away in the trash (don't compost it).