The kid left Russian Federation in January of 1992 which means that he did not live in Russia as of February 1992. I do not know how he left Russia and whether he was de-registered before leaving - it makes a big difference. If I were him, I would apply for a citizenship verification. It takes time, but then he would get a definite answer from the embassy. I am a bit surprised they want to see the certificate of renunciation because it is not their usual practice.