How to calculate current consumption of this sensor?
The active ranging current is the current while measuring, the timing ranged inter measurement value is the current when not ranging. To get the total current multiply the two currents by the proportion of time you will be in each of the two states.

Assuming it takes 33ms for a range then your average power consumption in mA is:
0.033*n*19 + (1-0.033*n)*0.016
where n is the number of ranges per second.

So for 1Hz (n=1) the average current will be 0.64mA. For 10Hz (n=10) it would be 6.28mA.

With a nominal voltage of 2.8V this gives a power draw of 17.6mW Vs the 20mW number given in the table. However the 20mW is a maximum current consumption. The operating currents don't state a maximum but the standby currents do, they indicate that the maximum can be 40-50% over the typical values. Applying the same margin to the transmit currents would give 24mW power draw maximum. This is too high but it is reasonable that it's an over estimate, standby current is largely due to leakage currents which are more prone to process variability than operating currents. If we were to assume that the max operating current was only 10% over the typical then we get:
Max current = 0.033*n*19*1.1 + (1-0.033*n)*0.016*1.4
Which for 10 Hz ends up working out as 19.4mW.

So with a little bit of hand waving and reasonable assumptions it all seems to just about add up. A maximum current of just over 10% of typical seems like a reasonable tolerance to me.