Black's last move was Rad8 (?) Adam now missed the best reply, both on his next move and the move after that. Although Adam went on to win after 57 moves, he could have probably forced his opponent to resign if he had found the best move. Can you see it?
Incidentally, after that first round loss, GM Sengupta went on to score 7/9 and share first place with Chinese IM Yiping Lou.