You didnt said much but it seems that offended him. His reaction was exagerated but he has more than 1k games and stays fine with warns so: !denied
Dont say something about someone else relative, maybe he loves his grandma more than you love yours and if you are going to say anyway then dont ask to be warned when he is replying something about one of your relatives too... My best advice here: if you dislike something then dont do that something to someone else.