Did a quick test and realized that tapping the top edge of the screen does indeed drop the notification shade. That's probably what is causing it. Perhaps due to your ear touching the top of the screen.
Well that was an interesting experiment. All I have to do is barely move my finger to the left of the sensor and the screen lights up. First phone in all of my years (2009 Original Moto Droid) of using and buying phones that this has been an issue. Well I guess I'll have to figure out some way of "Not using it that way" (Apple pun intended)