You needed to speak up, immediately. For that person's benefit, and everyone else. Presumably that person was routinely making sure everybody's air was on, but it ought to be done correctly. As you will likely learn, in the tec diving community, you do NOT touch someone else's valves.On my last liveaboard channel islands I completely set up my rig and had the air fully open went to grab something out of my bag and turned around and saw someone closing my air with my bcd on it to fully closed. I stupidly didnt say anything or make a scene but walked back and opened it fully again.