I'm not a doctor, but I know sometimes we will run high under stress because under great stress we will release adrenaline which works against insulin- so most of the time when I am under stress my blood sugars go high.
This is the same kind of stress that happens too when you exercise at an anaerobic level (like doing sprints or super heavy weight lifting)-your body witll release adrenaline which works against insulin.
So why do some people go low when under stress- I don't know- maybe it is a different level of stress- like you are not to the super level of stress physically, but stressed in a way that you are running around a lot, doing a lot of things, juggling a lot of tasks, and don't really realize it, but if you looked at your level of physical exertion it was a little bit more than normal (not anaerobic) and maybe you didn't quite have as much protein in your system to sustain your insulin and therefore drop low- that is why I usually go low-
Like yesterday, I was soooo busy, extra stuff at work so only had half of a measly turkey sandwhich all day before dinner so was a going low right before dinner (72)- even though I am on a pump- I just did a little bit more exertion than normal because all of my tasks and really did not have much food in my system.
I think that is why and when I go low under stress- but too much physical stress or intense stress- where my body releases adrenaline will make me go high,
Hope that helps!