As one who has ridden motos and horses in the woods for many years, I can say when most horses spook its because they sensed some uneasiness in their rider, I.e., the rider spooks first. I have a couple that you would have trouble keeping up with on tight single track, and they wouldn't care if you were behind them. A good horses is totally into the rider and isn't thinking on their own. That said, you will run into riders who do it infrequently and haven't bonded with their mount, and are already nervous. You come up on a motor and the rider is thinking train wreck and the horses senses that and reacts. They are a "flight" animal, on there own they will flee and then later when they think they are safe will turn around and look at what they were running from. As for the motos, the horses heard them and smelled them long before the rider did. Mountain bikes can be a different story.
So just be courteous and give them room. Look to the rider and see if he or she wants you to pass a certain way or stay stopped until the horses can walk past. I dont think you need to remove gear, the horse already knows your human and therider may want to just get the little meet up over with asap.