It is so great that you were there at the concert and noticed the situation. Had you not been there something horrible might have happened.
I doubt that the teen girls purposely placed the little Yorkie pup in harms way, I just don't think they were educated in the importance of taking care of such a breed as a tiny Yorkie.
I don't know the situation with the breeder but I do have concern that anybody would allow a 5 wk old pup to be adopted so soon. Hopefully there is a good reason for that, however we will never know.
I commend you for telling the girls about Yorkie Talk. I do hope they log on and learn all they can for their pup and also possibly keep in contact with you.
I really hope the future holds a devoted lifetime of love and care for this Yorkie.