What he meant was that social interaction is not just what people want, it is what they need in order to function. A polis was a Grecian city-state, an independent local nation. They were known for their strong sense of community, where every citizen had a voice when it came to politics, law and anything else that might affect their daily lives.
Today there are hundreds of thousands of polis' in existence.
You won't find them on a walk down the street or on your summer vacation. These local communities all exist on the World Wide Web. Some are dedicated to a specific topic, while others are more generalized. The trick is in connecting the two. The webmaster must provide the locality where this can all happen.