Actually it turns out that International Maritime Bureau had previously publicized that the ship had been hijacked and even provided coalition forces and other agencies with photographs of it.
India should leave pirate-hunting to professionals such as the coalition force who bother to set up links with civilian international bodies and cease its own, proven amateur efforts.
AFP: Indian navy destroyed Thai fishing boat, not pirate vessel: watchdog
Choong said that photographs of the Thai vessel had been sent out to the coalition naval forces and other agencies when it was hijacked as “the fishing boat was actually an ideal mother vessel for the pirates.”
Indian navy did not know that they are attacking a pirated ship. Indian forces are not part of the coalition to which the photos has been sent. They have the right to take action against a threat. Its sad loss of life.