The tool is based on a model of measured values, and is not showing the actual measurement.
The results are therefore estimates of the expected value. It is meant for evaluation purposes only, and will not give the exact numbers in every use case.
Testing shows that the estimated average current is typically within 5% of the actual value for the reference parts.
The device to device variations will add to this inaccuracy. Please refer to the nRF52 Product Specification for expected min/max values for the different current components.
If you experience any issues with this tool, please post a question here on Devzone. Any feedback is appreciated.