Ask HN: How does Twitter know who my family members are and why?

Yesterday I signed up for a new account on twitter using a third party browser(no active logins,incognito mode) on my phone. I used a new unused Gmail email id and selected a very vague twitter handle.

After completing signup the top two handles twitter recommended that I follow belonged to family members.

I was using the internet connection at home, which seems to be the only possible common link. It seems twitter uses ip addresses to track users. The accuracy disturbs me because I am pretty sure my dynamic home ip address resets a few times a day. Or perhaps twitter uses some other factors too but I cannot think of any other common points. My user agent,cookies and email id couldn't have linked me to my family members. Any thoughts? I was using my phone and my cellular data was on but since wifi was on it is preferred. My cellular carrier's website identifies my phone number but I doubt it would share my phone number with third party websites like twitter.