As a fellow adult with ADHD, I don't see how either of these "stereotypes," as you say, are harmful. Not understanding the effects of street drugs on a disease one does not have is hardly worthy of such contempt. If he had said something to the effect of "He was as unemployable as an alcoholic with ADHD," I could understand your indignation, but his remarks weren't disparaging, just mildly uninformed.

If you want to be offended, that's not really my business, but unless someone is responsible for your medical care or claims to know, I don't think it's fair to hold them responsible for this kind of information.