From what I've read, it seems like the hold letter means that the application will be reviewed again after May 15th because as of now, they haven't decided whether to accept or reject. After May 15th, the hold can either turn into a rejection or a waitlist spot, which is further broken down into the alternate list or the high priority list. Not sure if holds can go straight to acceptances or not.
Do you know when your friend interviewed? I'm still waiting to hear something. Thanks.