Well, my knee-jerk response is that they destroyed the evidence.
You didn't mention the actual statute which you are accused of violating. Since you were walking, I am assuming that it is Business & Professions Code (B&P) section 25620(a) which provides:
"Any person possessing any can, bottle, or other receptacle containing any alcoholic beverage that has been opened, or a seal broken, or the contents of which have been partially removed, in any city, county, or city and county owned park or other city, county, or city and county owned public place, or any recreation and park district, or any regional park or open-space district shall be guilty of an infraction if the city, county, or city and county has enacted an ordinance that prohibits the possession of those containers in those areas or the consumption of alcoholic beverages in those areas."
This is an infraction, not a misdemeanor. An infraction is not a crime. With very few exceptions, a "crime" is conduct which could expose you to custody time. An infraction calls for a fine. If you challenge it in court, you are entitled to a "court" trial, which is a trial where the judge is the fact-finder; there is no jury. I don't know the requirements for a real estate or contractor's license. However, if you plead guilty to the infraction you do not have to disclose it if your are asked whether you have been convicted of a "crime."