The conditions for Idrive current measurements in the data sheet are for a Vin = 0V. This means that the output codes are all 0s. If the output codes are toggling the current required to change the state of the SDO pin is increased and the Idrive current is increased. The worst case current will be when the conversion result is 101010.
The current drawn in a particular application will also depend on the capacitive load on the SDO line.