I'm sorry you had such a bad experience but to blame it on the breed or the dog is not the solution. If a dog acts like that then the owners are to blame.
Maybe you could give your friends some literature or videos from
Victoria Stillwell or
Caesar Milan that shows them how to turn their own and with that their dogs behavior around.
Just out of curiosity... why didn't you insist that your friends put their Yorkie back in the crate? Or if this was not an option, why didn't you leave?