As an EE, the following will make sense to you.

The house wiring system in a typical US home has two conductors at ground potential. One is a non-current carrying conduct which is called the grounding conductor, the other is a grounded current carrying conductor called the grounded conductor, or neutral. Both these conductors are connected to earth at the distribution panel OR, in case of mobile homes and such, at the service entrance.

Outside sourced signals over copper, such as the telco and cable signals, are generally not earth grounded at the same grounding electrode as the home distribution system. They are, rather, earthed at a remote location.

This sets up a situation where stray current can (and often will) travel in a circuit from the outside sourced system (say, down the cable wire) and out on the grounding conductor rather than the grounded conductor, and then (perhaps) also back to the remote system earth grounding electrode.

This is a bad thing. Bad house wiring isn't a factor, really.