Hi shourya,
Thanks for your detailed research on the ADP5090.
The quiescent current is not releated to the input voltage and input power, while it depends on the SYS voltage. And also, in cold start, we don't have the quiescent current sepc. which is specified when the cold start is completed. Since the cold start efficiency is very low, ADP5090 needs a minimum start up power like 16uW.
For the 10uW power after cold start, we just set some margins to keep the part work well especially for very low input votalge. If you are interested in the efficiency, you can see the efficiency curve in page 6 of the datasheet.
Regards,
Kevin