According to the sentencing judge, he was high on prescription drugs.  Not the beer or marijuana he told the cop about. 

"The state agreed to dismiss several other charges, including two additional accounts of assault, reckless driving and two counts of recklessly endangering another person."

http://www.oregonlive.com/pacific-northwest-news/index.ssf/2017/03/logan_kitzhaber_sentenced_to_1.html