Inductive pickup (foreign voltage) from even fairly long runs (20kf +) of well maintained copper is usually much less less than half a volt, measuring either T-R, or T-G/R-G. It's supposed to be floating to ground - nothing on a twisted pair should be ground referenced, if you do have voltage to ground, you have a short.
If it was not floating, you'd get atmospherics, hum, and other issues that you saw in old fashioned ground return systems.
Indeed, measurement of voltage and continuity of T-G and R-G is a standard way to check for faulty cable
Unless the telco cut the outer shielding on the twisted pair cables everywhere a terminal was installed. That was one of the remediations the incumbent had to undertake here when they started deploying 50Mbps VDSL2 FTTN service. Oops.
If it was not floating, you'd get atmospherics, hum, and other issues that you saw in old fashioned ground return systems.
Indeed, measurement of voltage and continuity of T-G and R-G is a standard way to check for faulty cable