@Francis,
Francis, his mother changed his name, but this may not have been a legal change of name, she may have just been calling him by a new name. I don't believe he had been reissued a new birth certificate with the adoptive mother's name on it. He flew back to Russia with his Russian passport.
I really don't think the adoption had been finalized yet. He had only been with the adoptive mother since September, 2009. I think that in the U.S. it takes a year before an adoption is finalized. When the adoption was finalized the child would have dual citizenship in the U.S. and Russia (the Russian citizenship would last until he was 18).
A finalized adoption cannot be undone at whim. If the adoption was finalized, and the mother wanted to give the child up, this would have to go through a court investigation and proceeding in the U.S.. She could not just abandon the child. If the adoption had not been finalized, she did have the right to notify the Russian agency to say she did not want to continue with the adoption. But that's not how this woman handled it.
I had friends who returned a child to an adoption agency before things had been finalized, and they had no problem doing that, although it was a heart breaking decision for them. They already had a biological child with serious physical disabilities, and the infant they were adopting also began displaying signs of serious physical disabilities. They just felt that managing two such children was more than they could cope with. The adoption agency agreed with them.
This child seems to have gone on two plane flights by himself--one from Tennessee to Washington, D.C., and then a flight from Washington to Moscow. They are questioning why the airlines allowed this unaccompanied minor to take these flights, and why immigration/customs allowed him to leave the country alone.