Excuse me, but why does it matter whether this murder is labeled "genocide" or not? I have a sneeking suspicion there's possible monetary reparations driving this semantic campaign-- "follow the money".
Actually it's all about legal definitions, but not in a way, like you've put it.
Genocide - contatry to "regular" murder - is not subject to time limitation.
That's why Nazis can still be braught to justice, no matter that they committed their crimes more than 60 years ago. "Regular" murderer is free, if not prosecuted within some period of time after his crime (in Poland it's 30 years).
Russians probably wanted to make it impossible to prosecute those perpetrators who are still alive, and that's why they deciced not to recognize that massacre as a genocide.