Why did Air India offload this activist from New Delhi to London flight?

Gladson Dungdung, an activist, was offloaded from an Air India flight AI 115 from New Delhi to London on May 9, 2016. The state-owned carrier told him his passport needs verification as it was impounded in 2013. He, however, says that his fight for the adivasis is what got him deplaned. 

Dungdung, however, has a different story to tell. He said, "I was going to attend the Workshop on Environmental History and Politics of South Asia to be held in the University of Sussex, UK on May 10th. The reason told to me is that my passport had been impounded in 2013, therefore, they will send it back to RTO, Ranchi for verification."

He said, "The fact is that my passport was impounded in 2013 and returned to me after proper verification in 2014. Thereafter, I had attended couple of international conferences in Denmark and London in 2014 and 2015 subsequently but there was no issue at all."

Dungdung said, "I m sure that this is a clear impact of my book 'Mission Saranda: A War for Natural Resources in India'."

"My fight for the Adivasis' ownership rights over the Natural resources, Adivasi identity, Human Rights, Ecology and against unjust development processes will continue till they take away my right to life forever. Jai Adivasi!" he concluded. 

While Air India did not respond to emails sent to them, an official said that the airline wasn't involved as Dungdung was stopped at immigration when he proceeded to check in.