The 64000 ton figure is pure speculation. The Indian navy has not said anything about the size of any third carrier, AFAIK. If you read this article -
http://www.indiandefenceforum.com/index.php?topic=12514.0 you will see that Admiral Mehta says nothing about either the size or delivery date (2017 is optimistic even for a carrier of the same design, BTW, let alone a much larger ship, necessarily of a new design), only saying that India will order another carrier.
Sengupta has a poor reputation. In this particular case, note this - "the US offer, made late last year, to lease to India for a 10-year period the conventionally-fuelled aircraft carrier, the 81,780-ton USS Kitty Hawk". There is no evidence for this claim. The US Secretary of Defence thought a reporter was joking when he was asked about it, in February this year. The story didn't even get an official denial for some time, because it was considered too silly, too obviously false, to be worth denying. The story began as a journalist speculating about the possibility of such a deal, & mutated on the internet into a story that the USA had made an offer. And yet Sengupta presents it as fact!