Tried it, result is very good after just a week, using apple cider vinegar, apply very liberally( splash it on) before bedtime, smell soon goes. Greasy skin feels dry but not dry as when using BP. Please try it.
It is a very old remedy for acne and it might be that is just what he needed to cure his acne. Also, a cure for something( anything) is normally close at hand, eg. get stung by nettles and there'll be dock leaves nearby. Vinegar for acne? sounds good to me.