When Aang expressed his disappointment at the ruins, he assured Aang that the Fire Nation did not destroy everything and led him to a hidden chamber of statues of past Avatars, each one representing his reincarnations over the years. Avatar Roku was his last life. Aang revealed that the airbenders knew he was the Avatar after he chose four toys out of a thousand, the same toys that belonged to the previous Avatars. It was then that Aang was told he could not have a family and had a responsibility to the four nations. During the ceremony where everyone bowed to him, expecting him to accept his role as the Avatar, he did not bow back.
The old man then apologized to Aang for luring him down there, as he had lived in poverty because of his absence. Confused, Aang turned to find himself surrounded by Fire Nation archers hiding behind the statues. Other soldiers poured into the chamber - one of them passed the old man a pouch of money as a reward, and he left.
The old man's betrayal of Aang is similar to the merchant in the "Relics" comic, who was also assigned at certain locations by Zhao to lure an airbender like Aang into a trap. Other similar story elements include Aang sneaking out from Katara and Sokka, and Aang using the practice area (a relic) to defeat Fire Nationsoldiers. In the novelization and an unused previz shown on the Blu-ray picture-in-picture, Aang used a different relic, large conch shells, to amplify his airbending against the soldiers, which is similar to the way Aang used the conch shell relic in the comic. However, the comic was written before the movie was released: the author/artist Johane Matte recalled checking the final colors for the comics in October 2009.
It is also similar to the way the old man whom Haru saved using earthbending betrayed Haru by reporting this to Fire Nation soldiers, resulting in Haru's arrest.