Ashing someone else's joint

I've been a daily smoker for over 20 years now, With joints as my preferred way of smoking. Well, we were at an event this weekend and after being passed a joint i noticed the ash was rather long on it, maybe ¼ of the remaining joint. Before i passed it to the next person I ashed it, not crushing it or anything like that. Just tapping it against my finger just hard enough to seperate the ash from the rest of it. As i was doing that, the person I was with kinda whispered in my ear "don't ash it, don't ash it" with some urgency. It was too late by then though. Nobody else said anything about it, nor did he for the rest of the event. But then, when we got in the car to leave he was like "man, i can't believe you ashed his joint" and tried explaining to me that its disrespectful for some reason. So reddit, did i commit a faux pas that i haven't heard of in my 2 decades plus of smoking, or were these just some pot snobs with their own little customs that nobody else has heard of? As far as ashing a joint, the only "rule" I've ever heard was "ash before you pass"