yeah no bueno......your buddy needs to lawyer up now! also depending on the state some DUI's with motor vehicles DO and WILL count against you, in a state like Minnesota where the speeding tickets are $500 for 6 over your buddy is and could be heading into a world of pain.
Did your friend willingly submit to a sobriety test in the park or was he stopped, was there consent given by your buddy? any witness's? time of day, what was the reason of the stop etc? there are some moving pieces here, shoot me a message.