In your video, you're still right in the middle. You didn't move over to the left wall. Plus, I tried that and still doesn't work. Closed door, open door, left wall, right wall, middle, crouching, standing, doesn't matter. Guard always gets question mark over his head. I believe it may be a bug.
You are so lucky that it works for you there because if it doesn't, you can't get that legshot exit. Haa!!!