I've had thisd exact same problem before. A friend rang me up one day and asked me if I had any weed (she also asked me if I could get any X.. I didnt deal either, but she couldnt get any and wondered if I knew anybody) and my mum was in the room and heard the whole convo and could tell what it was about even though i didnt mention drugs or anything. When I got off the phone she asked what that was about, I just said "just a mutual friend", when my mum asked what my 'friend' had wanted i just said "she was looking for some weed.. dont ask me why", then my mum asked who she was and i said "shit, i dunno.. i met her at a party a while ago but i dont remember her name coz i was drunk" my mum then asked "but why would she phone YOU asking for weed?" and i said "no idea.. shes probably just phoning anyone everyone she can think of" . my mum just said "oh" and that was the end of the convo lol