There are rules of immigration in every country; although most Indians think those rules only apply when they want to settle in other affluent countries. There is legal immigration and then there is just crossing the borders because they ae porous. In Mr. Subba's case, it appears he just entered the country and never seem to have filed proper papers. For example there are several Indians that have taken up citizenship in other countries; unfortunately they are not eligible to contest these elections eventhough they were born and brought up in India.
These are rules; must be followed properly, though they sound assenile at times. Mr. Subba must also follow them. Although, he can always buy a birth certificate for a small price to declare his citizenship status. This shows the level corruption all around!