Not necessarily, I have seen plenty of unbalanced circuits which use a pair of conductors & a screen.
But, of course, this doesn't make your comment invalid.
True enough. But that is NOT the scheme presented by the OP. Else we wouldn't be still discussing this.
Interestingly, in my experience, it [telescoping shield] is fairly unusual in Broadcast work,
It is rather a common technique.
Refer to the "Bible" of the audio interconnection world, Rane Note 101 "Sound System Interconnection"
https://www.rane.com/note110.htmlIn Figure 4. Interconnect chart for locating correct cable assemblies...
Note in particular connection diagrams# 1, 2, 5, 6, 7, 8, 11, 12, 13, 14, 17, 18, 23, and 24
More than half of the diagrams show telescoping shield schemes where the shield is connected on one end only.
As you observed, ALL of them feature a second inside wire which provides the return path for the audio circuit.
And the examples here show both balanced AND unbalanced interconnections.
In ALL cases where a single-conductor shielded cable is used, the shield is connected on BOTH ends.
Note in particular, scheme # 20 which is RCA to RCA.