Apart from the 120 days for violating probation (as stated in the article) the DA needs to see if they can nail him for under age drinking. Separate crime from probation violation (I think, not an atty). I'm sure that they can get someone from that party to fess up. Of course, the family can (maybe has) pay everyone at the party to keep their mouth shut.
Being told you're delusional does not necessarily mean you're mental.