Like Trenton, I have lived in coyote country all my life, and have never felt like one had any intention of attacking me. I don’t consider them to be cowards, and if I had one backed against a wall, I’m sure it would attack me if it saw no other option. When my dog Lupe was a young puppy border collie, it was not unusual to see a coyote tracking her as she would accompany me at our archery club, looking for lunch, no doubt, but as long as she was with me, the coyote would keep its distance. Now that she is close to being their size, they aren’t interested in her anymore. They become habituated to humans at places where they are protected, like Yosemite, and often approach people looking for handouts. I would never give a handout to a coyote in a million years, but other people do, and it is rare that you hear reports of anyone getting bitten. My first guess would be that the one that growled at your friend was sick, or else he misinterpreted what was happening.