Nyquil, mouth wash, hair tonic, after shave, and sterno all contain alcohol and alcoholics will and do use them in a pinch!
Most beer has less then 10% alcohol! So you tell me, is he drinking or not?
As already said go with your gut, there are hundreds of alcohol free meds over the counter that are alcohol free.
IMO he is drinking, whether it is Nyquil alone or Nyquil to cover other drinking I don't know, but half a bottle (That you know of) a day is WAY WAY beyond the daily reccommended dosage.