It means that he was given PC1000 "diversion" in the the case. If he had successfully completed diversion, the case would have been dismissed on 4/21. He fell out of diversion and went out to warrant, so the 4/21 date was vacated. He still needs to address the case, because he pled guilty to a felony and now needs to be sentenced.
Any statements I make in these forums (fora?) should not be taken as direct legal advice, merely informed guidance. This is true due to the anonymous nature of this venue, and the incomplete information which is invariably provided by the questions. It is imperative that you consult directly with an attorney regarding your specific situation before acting on or relying on anything represented here. Period.
It sounds like the hearing will not be held regarding the diversion program he was on. He needs to get a lawyer to deal with this.
The language you presented sounds like he is going to have a diversion hearing. Get an attorney.
ANDREW ROBERTS CRIMINAL AND TRAFFIC TICKET DEFENSE ATTORNEY