When the Mass was standardized after the Council of Trent, all Rites that at that time had been celebrated for more than 200 years were able to continue. So, if the Catholic Churches in India had had their own Rite, they would have been able to continue using it.
But the folks who went to India may have not had a clear understanding of all the rules of the Tridentine Rite.
It was a Papal delegation or a Vatican delegation with Apostolic Annunico. Probably just some Portuguese priests trying to re-unite Catholics who have not been in contact almost since the first century.
Think of the communication problems we have in the 20th and 21st centuries, and we have all sorts of technology to aid us.
For communication in those times, it took months for news of things to reach one end of Europe to the other.
Let alone correct news going from India to Portugal to the Vatican.
Council of Trent took place in 1563.
The arrival of the Portuguese was in 1498 -- a few years after Columbus discovered America -- the West Indies, other parts of America -- on his four voyages of discovery.
A good (and much more accurate link) on the Saint Thomas Christians and the contact with the West in 1498 is the following:
Profiles of the Eastern churches: The Syro-Malabar Catholic Church (by Michael J.L. La Civita)
This is an article by:
CNEWA -- A Papal Agency for Humanitarian and Pastoral support.
This article explains the "POLITICS" of what happened...