I'm the one with the staff. The other guy's gaming name is "kasai." Yes, when you're using a staff, arm shots are your second biggest weakness (with any large weapon, being rushed is the worst thing that can happen)... but he was going for the arms a few times in that exchange... he struck at my arm at :01, my chest at :02, chest again at :03, and his down fall was being too aggressive going for my arm at :04...
At that moment I noticed he was closing too much distance, backing me into a corner, and going for my arm, so I needed to block the arm shot with the back end of the staff, while dropping the front end down so I can thrust (an unlikely attack to hit, mostly just to get my distance back). Unfortunately, he was coming in too quick and when I tried to drop my weapon in front of him to get ready to thrust... his head was in the way...
With a staff, positioning is everything.