The datasheet is telling you that the device was tested with a shunt current of 5mA. The absolute maximum shunt current appears to be 25mA.
So, you should design the circuits that supply Vs assuming that the nominal current is 5mA but also guaranteeing that the current can never exceed 25mA. The datasheet provides several examples of how to do this.
@TimWescott makes an important point.
If you draw current from the 5V VDD output of this chip then that current will also be drawn from VS and you will need to design accordingly.
The maximum quiescent current (800\$\mu\$A) is specified for VS = 12V, meaning that no significant current is passing through the zener diode. If you design for VS = 17V then the quiescent current is likely to be much larger. I suggest you design your circuits assuming that the shunt current is 5mA when VS = 17V.