Re: xFi notification "New Device Connected"

This week a new device called Arris with no number connected to my modem I switched to XFi modem, changed user name and password. I called Comcast and the XFi modem was suggested. Then today I got a security threat about a guest who was in my home using their tablet so I guess the XFi is doing what it is supposed to. The Arris device which I was told was a modem that tried to connect to my system before XFi system had to be in close proximity cannot connect. Is this true that the Arris modem that tried to hack my system had to be close in proximity? I’m asking because I have restaurant behind me and I live in a apartment building? Sorry long winded!😊