I would be inclined to believe you if those granades would happen to land at approximate positions. It also doesn't seem fair for the aliens being able to use sound for calculating my teams position if I can't use the same mechanic for my own team.
If this behaviour really isn't a bug, then it's a bug that you as a player have absolutely no capability to use sound as well. The light scout drone going completely silent as soon as it enters a dark tile isn't really fair now, is it?
Also, the pinpoint accuracy EVERY time makes me believe it's not just approximates based on "sound" information. The AI throws their grenades always perfectly on your head. Meh, a hunter scout engine alone should be capable of masking a few footsteps in the grass shouldn't it?
In my honest opinion, I'm all in for more intelligent AI. However, based on testing, I don't believe grenade throws to be a result of intelligence. Just the simple fact that when throwing grenades, the AI always exactly knows where you are and NEVER misses.
EDIT: Also, if they're supposed to know my position so exactly, why don't they just shoot me with rifles instead?