A map of the world or a bridge of the world

The lunchroom was a ___ of the world.
A. map B. bridge
This is from a cloze test. The answer is A, butI cannot appreciate the reasons behind the use of it. I feel B is OK. What's your comment? Thanks.
The original article:

Need A Map?
Sharon Fleischer

It was my first day at school. I felt nervous and scared.
I went to all my classes with no friends. It felt like no one cared.
I listened anxiously to all the lessons and waited for lunchbreak at one. Then finally the bell rang. It was time to talk and have fun.

In the lunchline I met a new friend who wore a hijab on her head, and though I am Jewish, we got along fine, and I was so relieved when she said, "Sit with us, at our table." She pointed to the one next to the door.

So I agreed, and took my tray and was about to walk with her across the floor, when suddenly I felt a nudge. "Hey, I saw you on the bus," said a tall girl in a long skirt. "I see your Jewish star necklace. You should sit with us."

At that moment I looked around, and that's when I noticed, to my surprise, the nations of the world, isolating themselves. That's what I saw through my own eyes.

The Spanish only sat with Spanish, the Hindus only with Hindus, the Russians always with the Russians, and never the Arabs with the Jews.

I saw the reason why war gets started. Everyone sticks to their own kind. The lunchroom was a map of the world. Why was everyone so blind?

And so I turned down this girl, and went with the first, and there was no enmity. I built a bridge between two worlds when I sat with those different from me.