I believe the etiquette they are refering to is only for oncoming 'traffic'. How can you possibly 'yeild' to someone who is moving away from you?
I believe the proper thing to do is to yell 'Rider on your right/left' or 'coming up on your right/left'.
Yelling is alot less startling than having a full grown adult hurling at you with no warning at all!
As with horses, from my experience, noises dont startle them nearly as much as 'sneaking up' on them. Never ever sneak up on an animal, make it clear as day your coming.