They can tell your contacts by seeing who you contact, and when you contact them, how often, how quickly they respond, how long the connection goes on, whether

They can tell your contacts by seeing who you contact, and when you contact them, how often, how quickly they respond, how long the connection goes on, whether it's a lot or little data, voice or text, large or small data. They probably get a better view of your actual contacts than your address book ever has, they're just missing "dentist near my old home" and "aunt I never talk to".