It really depends. Alcohol charges are never truly traffic charges. Traffic consist of speeding, driving without a license, parking infractions, and incidents such as these.
Alcohol charges such as DUI and underage drinking are almost always "criminal charges." This being said it is a misdemeanor as opposed to a simple traffic charge. You may remember when he went through the ordeal...the general rule is that if jail time was a possibility, it was a criminal charge.
He has to answer this question based on what is asked. You didn't say if the charge was dismissed or if he was convicted...you only mentioned the other charge as being dismissed.
If he was convicted, then he has to report it as a conviction. If he was not, then he only has to disclose it if the question asks for charges and not convictions.