Strange, agreed. But horns do face forward, and their frequencies are much different. Plus it might have been a combination of being visible and sound. I don't have any reason not to believe him. I still say that, when it comes to deer, nothing is reliable or predictable.
I didn't hit the horn button until I knew I was safely past it. I don't think that it's a good idea to scare a animal that's already spooked. If it's moving in a direction, let it continue and don't distract it from doing that until you are clear of it. Otherwise, it may panic more, and reverse direction again, possibly into your path.
I've heard others tell tales of deer running into the sides of their cars / trucks, while driving down the road. I also saw the aftermath of a deer running into the side of a BMW motorcycle while the guy was riding down the road. He kept the bike upright, but it tore the right saddle bag right off the bike. It broke the mounts, so his buddy carried the bag back to town for him. They were able to strap it on with nylon tie down straps, so he could make it home.
Long story short, once they are spooked, they don't always look for what's coming, they just run. It's almost always safer to let them do that without distracting or scaring them more, and try not to get in their way.
