The reflection is only bidirectional if you can see the other person’s eyes.
It’s like if someone is in a bathroom stall. You could see the stall is occupied by seeing their feet stick below the wall of the stall, but they cannot necessarily see any part of you since their eyes are not where their feet are.
Same principle applies to reflections, where maybe the body part that you can see is just the top of the head, and since the person isn’t tall enough they can’t see that you can see them.
The reflection is only bidirectional if you can see the other person’s eyes.
It’s like if someone is in a bathroom stall. You could see the stall is occupied by seeing their feet stick below the wall of the stall, but they cannot necessarily see any part of you since their eyes are not where their feet are.
Same principle applies to reflections, where maybe the body part that you can see is just the top of the head, and since the person isn’t tall enough they can’t see that you can see them.