Yes - If she is giving him that point of view (which, though I agreed before is fairly irresponsible for a 14yo, I also explained why I advocate realsitic drug education) and you know about it, at least you can give him the other side of the story.
BE CAREFUL though - if you go all out onto a 'drugs are bad' rap with him, he wont listen.
If my mother told me something, and someone else told me the opposite, i have to say i;d probably side with my mother, so chances are he will too.
Maybe you could try to be more liberated, he is obviously a very confident young man to feel he can tell you that he drinks and smokes weed. That should be embraced, as honesty in teenagers is something most people strive for.
If he is telling you what he is getting up to, at least you can try to educate him on how to do it safely.
Possibly thats what his mother is doing? Although I agree with you about the cocaine thing.. its really not particularly dangerous.. Certainly ecstacy is more dangerous than cocaine. BUT, most drugs are generally, fairless harmless (short term) and the chances of one pill, or one line, or one joint doing you ANY harm is tiny.
Telling him this is her choice. Personally, I think he is a little too young, but he does sound quite mature so if the mother feels the time for drug education is now, who are we to judge?