Dolphins use echolocation to survive in the ocean, to a dolphin that is a map using a wave of sound to find a friend. You could hear a dolphin's sound wave from here in Sandhurst to Cornwall.
As well as being friendly they also have to have a defence weapon. Most dolphins don't have sharp teeth so they use their bulging tails and flippers which could kill a human being.
Friendship matters to a dolphin especially river dolphins who hunt and travel in a pod. If any dolphin had no friends you'd be staying on the outside of the pod where you are not protected against sharks or any other large predators.