"He didn't really spook at that."
Horses are naturally spooky animals. They startle very easily - and have to be trained out of it.
But horses will sometimes fake a spook - pretend to be afraid of a harmless object. Working horses with heart rate monitors show that this form of equine "lying" does exist - they spook, but their heart rate doesn't alter. If you really know a horse, you can sometimes tell a fake spook from a real one - some horses do different things with their ears.
Why would a horse do that? The most common reason is that it's an evasion - they want to get out of work. By pretending to be scared, maybe they can convince their rider they have a good reason not to go down the longer trail rather than the shorter one. I've also known horses I suspect of doing it just to annoy their rider because they're in a bad mood or being asked to do something they'd prefer not to.