Hi Saurav,
Could you confirm if you have also tried a similar request using the Keywords Planner in the AdWords UI? If you haven't yet, I would recommend that you do so and if the results match then it would mean that the "world" query indeed results to a high estimate value.
However, should you encounter any discrepancies, kindly send to me your clientCustomerId, the generated SOAP request and response and the screenshot of the Keyword Planner so I can further investigate. You may reply via Reply privately to author.
Best regards,
Peter
AdWords API Team