It was probably from a peck someone received while traveling. A couple of respiratory diseases can cause bloody mucus from the nose, but there would be lots of it. The chickens would be having coughing, sneezing, lots of snots and looking very bad. Watch for any bloody droppings too since one may have stuck their nose in it. I probably wouldn't worry about it unless you see more. The best time to handle your new chickens will be after dark in their coop when they have gone to roost. Checking them for lice and mites under their vents at the base of the feathers, and worming with a good wormer like Safeguard liquid goat wormer would be good to do with new chickens. Good luck, you will enjoy them.