You glance left brieflyYou switch to your bow landing momentarily on your torch
The eye starts to open due to your lightsource (this should have told you something could see you with the torch)
You draw back on the bow
The zombie from under the stairs growls (You hear it while the green bar is filling up and you are drawing the bow).
I agree that there was an element of inaccurate information as the stealth eye did go back to undetected and there were no movement noises by the zombie that killed you and the growl was not loud as from something close by. I still say that if you are playing dead is dead and you see that eye move
at all it is always best to do a quick look around especially if you accidentally pulled out a light source. What killed you was your desire to kill that sleeper right then and there. As I said, I sometimes fall into the same trap. I ignore safety because I really want to complete whatever objective I set for myself in that moment.