that alcoholic definition is the one based on habitual alcohol consumption, and it becoomes habitual if you drink once a week or once a month (although it does not fit the general picture people have of alcoholics).
As for mixing, I must admit I have a horribly fine sense of taste, so cocktails and mixed drinks don't meet my tastes as well. I know that in theory the danger n mixed drinks lies in not noticing the alcohol you consume, but for me I still have to find a mix where I don't notice the degradation of taste.