When meeting strangers in the street, you don't just say "Hi" in the streets of China. You have to have greetings + something to call them as a basic respect in China, and these greetings are family related. For example if you meet a senior citizen in China will say, "Hello Grandfather".
Other examples would be referring to people as Uncle, or Aunts, or big brother or little sister depending on your apparent age relation to others.