I would do nothing and here are my reasons. A disorderly conduct charge is a simple 2nd degree misdemeanor. Nobody takes it seriously. In your son's case, the charges were dropped, so no conviction. It won't keep him from being employed, joining the nilitary, from owning a gun, or from getting a professional license. At age 25 it is supposed to be expunged anyway. If he stays out of trouble from here on out, he will be okay. If he doesn't, you may want that expungement for a more seious crime. Good luck.
Normally I would agree with Don and advise you to do nothing, but because your son did a Juvenile Diversion program, he may be eligible for a specific expungement provision that would not prohibit him from also moving to seal or expunge something else in the future.
So go hire a good attorney and ask him to explain juvenile diversion expungement to you; and teh pros and cons of moving forward on it.