A couple of years ago a lady in my neighborhood was attacked by three half-grown pit-bull puppies (they weren't more than 9 months old.) They were about 30-35 pounds each, so a bit smaller than any of the coyotes I've ever seen. I was the second person on the scene and had the misfortune of seeing the results of their attack: they had grabbed her by the arms and dragged her down to the ground, and then bit and tore at everything they could reach. She had extensive, very deep wounds everywhere. So I can see how a couple of slightly larger coyotes could kill a lone human.
I love dogs, and have much respect for all of the canids. But it's a little frightening to see what they are really capable of when they work together as a pack.