What does this circuit show?
Yes, it's showing a "10x" oscilloscope probe and the input it is connected to.

I imagine the point is to explain how a 10x scope probe works.  This includes not just the 10x attenuation at DC, but also how the capacitors cause the same attenuation at high frequencies.  C1 is the probe "compenstation" capacitor.  This diagram sets things up to explain what it's there for and how it works.

The reason for showing the cable is probably to point out that there are unpredictable things going on.  You don't know the capacitance of the cable, for example.  The text probably explains how C1 should be computed, but I expect also then explains why you can't know it exactly up front and it needs to be quite accurate, and that this is therefore implemented as a trim cap that the user has to set.