Undoubtedly it was a plea bargain which is not a real guilty plea.  Likely he was charged with a whole laundry list of crimes that would have put him in jail for many many years.  They then offer to drastically reduce the charges if he will plead guilty.  Meanwhile his defense lawyer offers to fight the original charges like gang busters but in the end mutters that he can't guarantee acquittal even if innocent as jurors often believe the DA just because the DA represents the people.