What is the difference between a DUI and zero tolerance?

my friend was pulled over for having drank a little and drove. The officer also found close alcohol a couple cans of beer in the car. He left the station and was given a ticket for "light above license plat being out" lame excuse for pulling him over, and for transporting alcohol. Thats all he was given does that mean in court he is going to get a DUI/zero tolerance? Did the officer make a mistake by only giving him 2 citations and no DUI? Last what is the difference in a DUI from zero tolerance? it happen in cook county Illinois.