There may be a bit of "communist math" there, but I tend to believe the Soviet sniper statistics overall, for a couple of reasons.
There was a "sniper cult" in the Red Army at the time, and a lot of emphasis was given to sniper training, recruitment, tactics, and so on. To be sure, it was heavily hyped by propaganda, but there was a was a real attempt to make sniping an effective combat technique.
Also, and perhaps more importantly, the nature, scope, and duration of the war in the East afforded many opportunities for snipers, especially in comparison to other theatres. Long sieges of cities (Stalingrad, Leningrad, Sevastopol), partisan warfare (Ukraine, Belorussia, many other areas), protracted defense of fortifications (Moscow, Kursk), all made for an environment where the effectiveness of snipers would naturally be utilized.