Criminal Law Dismissed charge and I 485

[poor_one]

My husband had a charge of hit and run. He was never finger printed or had his picture taken. He was just cited for the incident and had to go to court. The charge was dismissed. He only had to pay the court cost. How will this affect the I 485. Is this an arrest? I understand that it is not a conviction. But, do we need to report this as an arrest?

PLEASE, YOUR HELP WOULD BE VERY MUCH APPRECIATED

Thanks for your help in anticipation.
poor one