How does telegram promote new people you might know?

I'm always amazed at the randomness of people that telegram reports. I get in my normal list of conversations "[Bob Smith] joined Telegram". Where Bob Smith is sometimes: 1) an actual person in my phone's contact list 2) a person two degrees away (friend of a friend) 3) a person geographically close (neighbor) but sometimes 4) person I once did something with once on some site long ago OMG how does telegram know to link us????