Yes, but if you click on your friends profile links and then on theirs and so on, Murray is suggesting that you can end up quite far away. I have tested this and it does seem to work.
This isn't new though, there is the 6 degrees of separation (which has been tested up to a maximum degree of 13). So, logically, if everyone on Earth had a Facebook account, after clicking through 13 times, you could end up at anyone in the world you wanted to find.
Also, people joining a craze and joining a group because someone else has is explainable through social conditioning. Humans are social animals and have the need to create bonds and relationships. People drink, smoke and give in to peer pressure or accept hazing as part of becoming socially accepted.
Healthy humans should have a friend base of 120-150 (below that and humans will try to fill those spaces, above that and humans will start prioritising friends and caring for others much less. Anyone outside the favoured 150 people are not going to receive much attention or care).
When you copy someone, agree with someone or try something out because a friend has (or if you join a Facebook group because a friend has), then you are creating a mutual bond. Most of the time, they lead to nothing.
If you find someone and recognise that they are wearing a shirt of the band you love and their not a popular band, there will be a need for mutual bonding because of it.